PHYSICS 

RAMMAR  SCHOOLS 


HARRINGTON 


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Southern  Branch 
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University  of  California 

Los  Angeles 


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PHYSICS 


FOR   GRAMMAR    SCHOOLS 

67/f 


BY 

CHARLES   L.    HARRINGTON,    M.A. 

HEAD  MASTER  OF  DR.  J.  SACHS'S  SCHOOL  FOR  BOYS,  NEW  YORK 


NEW  YORK- :•  CINCINNATI- :•  CHICAGO 

AMERICAN    BOOK    COMPANY 


COPYRIGHT,  1897,  BY 
AMERICAN  BOOK  COMPANY. 

HARRINGTON'S  PHYSICS. 
W.  P.  2 


PREFACE. 


THIS  book  is  the  result  of  several  years'  use  of  the 
experimental  method  in  teaching  physics  to  boys  under 
thirteen  years  of  age.  It  considers  subjects  which  are 
full  of  interest,  and  it  compels  the  student  to  do  work,  to 
observe  carefully,  and  to  write  an  accurate  account  of  his 
observations.  In  the  case  of  every  student  it  is  found  to 
awaken  dormant  energy  and  to  arouse  enthusiasm.  After 
a  lapse  of  three  or  four  years,  when  the  student  begins 
the  more  earnest  work  of  preparing  for  college  science 
examinations,  he  finds  himself  acquainted  with  many 
fundamental  facts  and  ready  to  advance  rapidly. 

The  book,  although  preliminary,  follows  the  method 
indicated  in  the  requirements  for  admission  to  Harvard 
and  Columbia  Universities,  and  contains  only  such 
experiments  as  have  been  found  by  the  writer  to  be 
serviceable. 

The  experiments  set  for  the  student  should  be  per- 
formed at  home,  and  notes  of  his  observations  should  be 
written  on  slips  of  paper.  During  the  recitation  periods 
the  results  obtained  by  the  several  students  should  be 
compared  and  criticised,  and  the  correct  results  then  and 
there  written  in  the  blank  spaces  left  for  the  purpose  in 
this  book.  Two  recitation  periods  per  week  for  forty 
3 


4  PREFACE. 

weeks  will  be  ample  for  performing  in  this  manner  all 
the  experiments. 

The  experiments  to  be  performed  by  the  teacher  should 
be  closely  observed  by  the  students,  and  then  they  should 
state  the  correct  results. 

The  writer  hopes  that  his  fellow-teachers  will  derive  as 
much  pleasure  as  he  himself  has  obtained  in  watching  the 
rapid  growth  of  mental  effort  under  this  method  of  work. 

C.   L.    HARRINGTON. 

38  W.  59TH  ST.,  NEW  YORK. 


CONTENTS. 


PAGE 

I .    MATTER  —  MASSES  —  MOLECULES  —  ATOMS  —  SPACES 

BETWEEN  MOLECULES      .        .        .        .        .        .        7 

CONDITIONS  OF  MATTED  —  CHANGES  IN  MATTER        .       12 
SOME  PHYSICAL  PROPERTIES  OF  MATTER  .        .        .       16 
WORK  —  FORCE  —  GRAVITY        .        .        .-.•'.      21 
V.    CENTER  OF  GRAVITY  —  FALLING  BODIES    ....      26 

VI.     PENDULUMS .        .        .        -31 

VII.     LEVER  —  WHEEL  AND  AXLE  —  PULLEY      .        .        -35 
VIII.    ATMOSPHERIC    PRESSURE  —  PRELIMINARY     EXPERI- 
MENTS        47 

IX.    ATMOSPHERIC  PRESSURE  —  THE  SIPHON     ...      50 

X.    ATMOSPHERIC  PRESSURE  —  PUMPS  FOR  LIQUIDS         .      53 

XI.    ATMOSPHERIC  PRESSURE  —  PUMPS  FOR  GASES    .        .      58 

XII.     MAGNETISM 65 

XIII.  FRICTIONAL  ELECTRICITY 71 

XIV.  CURRENT  ELECTRICITY        .        .        .        .        .        .80 

XV.    ELECTRICITY  DEVELOPED  BY  MAGNETS  AND  BY  CUR- 
RENTS        86 

XVI.    MOVEMENT  OF  LIGHT  .        .        .        .        .        .        -93 

XVII.    VIBRATIONS  —  SOUND 104 

XVIII.    HEAT  —  EFFECTS  OF  HEAT no 

QUESTIONS  IN  REVIEW 116 

APPENDIX 119 

5 


MATTER -MASSES -MOLECULES -ATOMS -SPACES   BETWEEN 
MOLECULES. 

Experiment  1.    Put  as  much  water  as  possible  into  a 
goblet,  and  drop  a  stone  gently  into  the  water. 


Exp.  2.    Try  to  put  any  two  objects  into  the  same  space 
at  the  same  time. 


Exp.  3.  Push  an  inverted 
goblet  into  water,  holding  it 
firmly. 


Why  does    not    the  water 
enter  the  goblet  ? 


Fig.   1. 


8  MATTER. 

Suppose  you  have  two  things  that  can  be  handled ;  can 
you  make  either  occupy  the  same  space  as  the  other  at 
the  same  time  ? 


Definition.  —  Matter  is  that  which  occupies  space  and 
prevents  other  matter  from  occupying  the  same  space  at 
the  same  time. 

Exp.  4.  Place  in  the  sun's  rays  the  goblet  of  water  of 
Exp.  i. 

Sunlight  occupies  space.  Do  you  think  from  Exp.  4 
that  sunlight  is  matter  ? 


Is  all  matter  visible  ? 


Name  any  invisible  matter. 


How  many  senses  have  we  to  help  us  in  learning  about 
matter  ?     Give  names. 


Exp.  5.    Break  a  lump  of  sugar  into  small  pieces.    Grind, 
or  pound,  some  of  these  pieces  into  a  fine  powder.     Dis- 


MASSES  —  MOLECULES. 


solve  some  of  this  fine  sugar  in  water.     Can  each  particle 
of  powdered  sugar  be  seen  with  the  naked  eye  ? 


Can  the  particles  of  dissolved  sugar  be  seen,  either  with 
the  naked  eye  or  with  a  microscope  ? 


NOTE.  —  These  particles  of  dissolved  sugar  are  the 
smallest  possible  particles  of  sugar ;  they  are  called  Mole- 
cules of  sugar.  The  chemist  can  obtain  from  these  mole- 
cules particles  smaller  than  the  molecules,  but  these  new 
particles  will  not  resemble  sugar  in  any  respect ;  they  are 
called  Atoms.  Thus  molecules  are  made  up  of  atoms. 

Most  scientists  believe  that  nothing  smaller  than  an 
atom  exists. 

Definitions.  —  A  Mass  is  any  appreciable  quantity  of 
matter. 

Illustrations.  _ 


A  Molecule  of  any  mass  is  the  smallest  possible  quantity 
of  that  mass. 

Illustrations.  _ 


Exp.  6.  Pour  sand  into  a  jar  filled  with  marbles  (or 
small  stones)  until  no  more  sand  will  enter.  Then  pour 
in  water  until  no  more  water  will  enter. 


10 


MATTER. 


Why  do  not  the  marbles  run  over  when  sand  is  poured  in  ? 
Why  do  not  the  marbles  and  sand  run  over  when  the 
water  is  poured  in  ? 

Because  in  the  first  case  there  are 


in  the  second  case  there  are 


Exp.  7.    Slowly  drop  a  little  fine  sugar  into  a  cup  as  full 
of  water  as  possible. 

Why  does  not  the  water  run  over  ? 


Exp.  8.    Heat  a  tumbler  of  cold  water  by  placing  it  in 
the  sun's  rays  or  near  a  stove. 

Where  have  the  air  bubbles  which  appear  been  hiding  ? 


Exp.  9.  Half  fill  a  small  bottle,  or  test  tube, 
with  water;  carefully  pour  in  alcohol  until  the 
bottle  is  full.  Close  the  mouth  of  the  bottle  with 
the  thumb,  and  shake  the  bottle  until  water  and 
alcohol  are  mixed. 


Fig.  2. 


SPACES    BETWEEN    MOLECULES.  n 

Why  is  the  bottle  not  full  after  alcohol  and  water  are 
mixed  ? 


We  may  now  understand  that  there  are  spaces  between  the 
molecules  of  all  kinds  of  matter. 


II. 

CONDITIONS  OF  MATTER-CHANGES  IN   MATTER. 

Experiment  10.  Try  to  separate  the  molecules  of  a 
piece  of  wood;  of  a  piece  of  iron;  of  some  water;  of 
some  mercury ;  of  some  air. 


Definitions.  —  A  Solid  is  a  body  whose  molecules  cling 
together  with  great  force. 

A  Liquid  is  a  body  whose  molecules  cling  together  with 
little  force. 

A  Gas  is  a  body  whose  molecules  do  not  cling  together, 
but  are  all  the  time  trying  to  get  away  from  each  other. 

A  Vapor  is  a  gas  which  at  ordinary  temperatures  changes 
either  to  a  liquid  or  to  a  solid. 


CONDITIONS   OF   MATTER.  13 

Name  three  solids. 

Name  three  liquids. 

Name  three  gases. 

Name  a  vapor. 

Name  the  three  conditions  of  matter. 


Exp.  11.  Place  a  piece  of  ice  in  an  iron  spoon,  and 
hold  the  spoon  over  a  flame.  Ascertain  whether  or  not 
the  ice  can  be  changed  into  water,  and  the  water  into 
a  vapor. 


NOTE.  —  Hot  (above  212°  F.)  vapor  of  water  is  called 
steam.  Steam  is  invisible. 

Warm  (below  212°  F.)  and  cold  vapors  of  water  are  gen- 
erally visible,  and  are  called  clouds,  or  fogs. 


I4  CHANGES   IN    MATTER. 


May  iron,  gold,  wood,  paper,  and  cloth  be  changed  as 
the  ice  was  changed  ? 


Exp.  12.    Move   a   book   from   place  to   place.     What 
change  is  made  ? 


What  change  was  made  in  the  sugar  in  Exp.  5  ? 


What  change  was  made  in  the  ice  in  Exp.  1 1  ? 


Name  the  three  changes  in  matter. 


Are  the  book,  sugar,  and  ice  of  the  same  nature  as  they 
were  before  any  change  was  made  ? 


Definition.  —  Any  change  in  a  mass  which  does  not 
involve  change  in  the  nature  of  the  mass  is  called  a 
Physical  Change. 


PHYSICAL   CHANGES.  15 

State  several  illustrations  of  physical  changes. 


Exp.  13.    Experiment  for  the  purpose  of  discovering  any 
physical  changes  which  have  not  been  mentioned. 


III. 

SOME    PHYSICAL    PROPERTIES    OF    MATTER. 

What  is  your  property  ? 
That  which... 

What  is  a  property  of  matter  ? 
That  which  . 


Exp.  14.    Repeat  Exp.  7,  and  ascertain  how  much  sugar 
can  be  added  without  making  the  water  run  over. 

teaspoonfuls. 


Definition.  —  Porosity  is  that  property  of  matter  by  which 
a  body  has  pores ;  that  is,  spaces  between  its  molecules. 

Exp.  15.    Hammer  a  piece  of  lead  (or  wood),  and  ascer- 
tain whether  or  not  it  becomes  smaller. 


Definition.  —  Compressibility  is  that  property  of  matter 
by  which  a  body  may  be  compressed,  or  made  to  occupy 
less  space. 

Exp.  16.  Obtain  strips  of  rubber,  wood,  copper,  iron, 
and  zinc.  Pull,  or  bend,  these  strips  out  of  shape. 

16 


FLEXIBILITY  — ELASTICITY.  \>j 

Definition.  —  Flexibility  is  that  property  of  matter  by 
which  a  body  may  be  pulled,  or  bent,  or  twisted,  out  of 
shape. 

Exp.  17.  Repeat  Exp.  16,  and  ascertain  which  of  the 
bodies  will  resume  their  first  forms  after  stress  upon  them 
is  removed. 


Definition.  —  Elasticity  is  that  property  of  matter  by 
which  bodies  tend  to  resume  their  first  forms  after  being 
changed  in  form  and  after  stress  is  removed. 

Which  of  the  bodies  named  in  Exp.  16  are  the  most 
flexible  ? 


Which  are  the  most  elastic  ? 


Rubber  is  one  of  the  most  flexible  substances  known.     Ivory  and 
glass  are  among  the  most  elastic  substances. 

Exp.  18.    Obtain  pieces  of  stone,  glass,  copper,  and  zinc. 
Try  to  scratch  each  with  each  of  the  others. 


HAR.   PHYS.  —  2 


t8  PHYSICAL   PROPERTIES  OF   MATTER. 

Definition. — Hardness  is  that  property  of  matter  by 
which  some  bodies  may  be  made  to  easily  scratch  other 
bodies. 

Exp.  19.  Try  to  break  pieces  of  glass,  wood,  copper,  or 
zinc  by  striking  them  sharp,  quick  blows  with  a  hammer. 


Definition. — Brittleness  is  that  property  of  matter  by 
which  some  bodies  may  be  easily  broken  by  a  sharp,  quick 
blow. 

Is  hardness  the  same  as  brittleness  ? 


Are  all  hard  bodies  brittle  ? 


Are  all  brittle  bodies  hard  ? 


Name  six  hard  bodies  which  are  not  brittle. 


QUESTIONS   IN   REVIEW.  19 

Name  six  brittle  bodies. 


Name  three  properties  of   matter  which  belong  to  all 
bodies. 


DEFINITION    OF    PHYSICS. 

Physics  treats  of  the  laws,  the  physical  changes,  and  the  physi- 
cal properties  of  matter. 

SUMMARY    OF    FIRST   THREE    CHAPTERS. 


Masses. 

Molecules. 

Atoms. 

Spaces  between  Molecules. 


Three  Conditions  of  Matter. 
Three  Physical  Changes. 
Some  Properties  of  Matter. 
Physics  Denned. 


QUESTIONS  IN  REVIEW. 

1.  What  is  an  experiment  ? 

2.  If  a  cubic  inch  of  iron  be  put  gently  into  a  goblet  full  (to  run- 
ning over)  of  water,  how  much  water  will  run  over  ? 

3.  How  might  you  find  the  size  of  your  body? 

4.  Is  an  atom  smaller  than  a  molecule? 

5.  When  a  pin  is  pushed  into  putty,  where  does  it  go  —  through  the 
molecules  or  between  them? 

6.  When  a  nail  is  driven  into  wood,  do  the  nail  and  wood  occupy 
the  same  space  at  the  same  time  ?     Explain  your  answer. 

7.  What  is  the  ordinary  condition  of  mercury? 


20  PHYSICAL   PROPERTIES   OF   MATTER. 

8.  How  may  one  prove  that  steam  is  invisible? 

9.  Name  some  properties  of  whalebone  ;  of  ivory ;  of  grass. 

10.  By  reason  of  what  property  of  matter  are  you  able  to  bend 
leather?     To  press  water  from  a  sponge? 

11.  Is  any  property  of  matter  illustrated  by  Exp.  3? 

12.  How  would  you  prove  that  gold  is  softer  than  iron? 

13.  When  a  rubber  cord  is  made  longer  by  stretching,  is  the  number 
of  molecules  increased  ? 

14.  If  a  quart  of  water  be  changed  into  steam,  will  the  number  of 
molecules  of  water  be  increased  ? 

15.  When  a  rubber  ball  is  thrown  against  a  wall,  is  the  ball  flattened? 

16.  By  reason  of  what  property  is  it  flattened? 

17.  What  causes  the  ball  to  rebound ?  • 

18.  Is  an  ivory  ball  flattened  when  thrown  against  a  hard  substance? 

19.  When  the  wind  blows  hard  against  a  large  pane  of  glass,  the 
glass  is  bent ;  why  is  it  not  broken  ? 

20.  Why  does  it  flatten  as  soon  as  the  wind  stops  blowing? 


IV. 

WORK- FORCE- GRAVITY. 

Experiment  20.  Try  to  move  your  open  hand  rapidly 
through  some  water  in  .a  tub. 

Try  in  the  same  way  to  move  an  open  fan  (the  flat  side, 
not  the  edge)  rapidly  through  the  air. 

Try  to  slide  on  a  stone  walk. 


Why  cannot  these  things  be  easily  done  ? 
Because  in  each  case  .  - 


NOTE.  —  Our  ideas  of  work  are  derived  from  the  actions 
of  our  muscles.  In  the  three  cases  just  mentioned  our 
muscles  were  at  work,  and  they  met  with  some  resistance 
in  doing  the  work.  It  is  evident  that  the  amount  of  work 
varies  as  the  resistance  varies :  a  large  resistance  calls  for 
a  large  amount  of  work ;  a  small  resistance  is  overcome 
by  a  small  amount  of  work.  More  work  is  done  in  sliding 
on  a  stone  walk  than  in  moving  one's  hand  through  water. 


22  WORK -FORCE -GRAVITY. 

Definitions.  —  Work  is  the  overcoming  of  resistance. 
Force  is  that  which  does  work. 

What  is  motion  ? 


What  causes  motion  ? 


Exp.  21.    Push  a  book ;  blow  against  some  small  pieces 
of  loose  paper. 

What  force  causes  the  motions  in  this  experiment  ? 


What  force  causes  molecules  to  get  farther  apart  ?    (See 
Exp.  8.) 


Name  any  other  forces  you  think  of. 


Exp.  22.  Suspend  any  object  by  means  of  a  string  held 
in  the  left  hand.  Cut  the  string  with  scissors. 

NOTE.  —  Before  the  string  was  cut  there  seemed  to  be  a 
pull  down,  caused  by  some  force,  and  a  pull  up,  caused  by 
muscular  force. 

Now  it  has  often  been  proved  that  any  two  masses 
attract  each  other. 


GRAVITATION. 

Thus  if  two  balls  be  prevented  from  falling 
to  the  earth,  their  mutual  attraction  may  be 
made  visible;  and  the  larger  the  masses,  the 
greater  their  mutual  attraction.  Two  large 
masses  of  lead,  when  suspended  by  long,  fine 
wires,  will  swing  toward  each  other  a  little. 

In  our  experiment  (22)  there  was  an  attrac- 
tion between  the  earth  and  the  object ;  before 
the  string  was  cut,  our  muscular  force  pre- 
vented their  moving  toward  each  other.  After 
the  string  was  cut,  their  mutual  attraction  caused 
the  object  to  move  toward  the  earth,  and  the 
earth  to  move  toward  the  object. 

Since,  however,  the  object  had  a  very  small 
mass,  and  the  earth  a  very  large  mass,  the 
object  moved  many  thousand  times  faster  and 
farther  than  the  earth. 

Definitions.  —  Gravitation  is  the  force  which 
causes  masses  of  matter  to  attract  each  other. 

This  mutual  attraction  is  called  Gravity  (for 
convenience)  when  the  earth  is  one  of  the 
masses. 

Weight  is  the  measure  of  gravity. 

NOTE.  —  It  is  evident  that  if  gravity  acts  at  a 
certain  place  with  a  force  of  one  pound  when 
an  object  has  a  certain  mass,  it  will  act  with  a 
force  of  two  pounds  on  another  object  which 
has  double  the  mass. 

We  must,  however,  distinguish  between  the 
names  mass  and  weight. 


Balls  of  lead 
each  weighing 
one  ton. 

Fig.  3. 


24  WORK -FORCE -GRAVITY. 

The  mass  of  any  object  remaining  the  same,  its  weight 
will  vary  according  to  its  place  on  the  earth  —  the  nearer 
it  is  to  the  center  of  the  earth,  the  more  it  will  weigh. 

The  North  Pole  being  nearer  the  center  of  the  earth  than 
is  the  equator,  any  mass  weighs  more  at  the  North  Pole. 
Again,  any  mass  weighs  less  at  the  top  of  a  mountain 
than  at  the  level  of  the  sea  or  at  the  foot  of  the  mountain. 

When  a  ball  is  batted  up,  why  does  it  not  continue  to 
move  up  ? 


If  gravity  were  half  as  strong  as  it  is,  how  high  could 
you  jump  ? 


Give  a  reason  for  your  last  answer. 


On  what  does  the  velocity  (rate  of  motion)  of  a  batted 
ball  depend  ? 


In  what  direction  does  a  body  move  when  acted  on  by  a 
force  ? 


PLUMB    LINE. 


Exp.  23.  Suspend  a  pencil  by  means  of  a  thread  or 
string,  and  ascertain  to  what  place  the  thread  points  when 
not  swinging. 


Definition.  —  A  Plumb  Line  is  a  straight  line  that  points 
toward  the  center  of  the  earth. 

What  workmen  use  plumb  lines,  and  for  what  purpose  ? 


It  is  evident  that  plumb  lines  are  not 
exactly  parallel,  since  each  points  towards 
the  earth's  center.  This  makes  no  prac- 
tical difference  when  the  plumb  lines  are 
not  very  far  apart.  In  the  latter  case, 
P.  plumb  lines  are  not  perceptibly  nearer  to- 

o.A.c.  and  d  represent  plumb  lines   Sether  at  their  lower  than  at  thdr  U?Per 
at  different  places  on  the  earth.       ends. 


V. 


CENTER  OF  GRAVITY  -  FALLING   BODIES. 


Side 
view. 


Fig.  5. 


Experiment  24.  Obtain  an 
irregular  piece  of  cardboard. 
After  making  two  pin  holes, 
as  represented  in  the  figure, 
suspend  a  plumb  line  from  a 
pin  stuck  through  one  hole, 
and  mark  on  the  cardboard 
the  direction  of  the  line.  Re- 
peat, using  the  second  hole. 
The  two  marks  will  cross. 
You  will  find  that  the  card- 
board may  be  balanced  on  the 
point  where  the  marks  cross. 


Definition. — The  Center  of  Gravity  of  a  body  is  the 
point  about  which  its  molecules  balance,  no  matter  what 
the  position  of  the  body. 


Exp.  25.    Repeat  Exp.  24,  using  a 
ring  of  cardboard. 

The  C.  G.  is  not  in  the. ... 


Fig.  6. 


CENTER   OF   GRAVITY. 


Exp.  26.    Stick  a  pin  through  a  cork,  and  fasten  two 
heavy  sticks  or  knives  into  the  sides  of  the  cork  (as  in 
Fig.  7).     Find  the  C.  G.   of  the  whole 
apparatus. 

The  C.  G.  is  below  the ._. 


Fig.  7. 


How  can  it  be  shown  that  the  ring  of 
Exp.  25  may  be  balanced  at  its  C.  G.  ? 


Draw  a  figure  to  show  in  what  line  the  C.  G.  of  a  chalk 
box  will  move  when  the  box  is  tipped  a  little  upon  an 
edge (ab}\  also  when  tipped  over.  Also 
to  show  in  what  line  the  C.  G.  of  a 
pencil  moves  when  the  pencil  is  tipped 
over. 

When  is  a  body  kept  from  tipping 
over  ? 

Fig'  8>  Ans.  When  its  C.  G.  is  supported. 

When  is  its  C.  G.  supported  ? 

Ans.  When  it  is  so  placed  that  it  cannot  reach  a 
lower  position  unless  acted  upon  by  some  force  other 
than  gravity.  Fig.  9. 


! 

C.O. 

1 

i 

/ 

28 


CENTER    OF    GRAVITY  —  FALLING    BODIES. 


Why  does  a  pencil  standing  on  end  continue  to   fall 
after  being  tipped  a  little  ? 


If  tipped,  why  will  the  object  represented  in   Fig.   7 
return  to  its  upright  position  ? 


When  is  a  body  easily  tipped  over  ? 
Ans.  When,  in  the  tipping,  its  C.  G.  needs 
to  be  raised  but  little. 

Exp.  27.    In  some  convenient  place  near  a 
board   (ab)  slightly  inclined,  suspend  a  stone 
by  means  of  a  string  39  inches  long.      Set  the 
stone  swinging  a  little.     Just  as  the  stone  be- 
gins one  of  its  swings,  let  a  marble  begin  to 
roll    down    the 
incline.     Ascer- 
tain whether  or 
not  the  marble  Fig.  10. 

will  roll  the  same  distance  during  the  second  as  during 
the  first  swing. 


FALLING   BODIES. 


29 


How  many  inches  does  the  marble  roll  during  the  first 
swing  ?      During  the  second  swing  ?      During  the  third 


i  st.  2d ...  ..  3d 

What  force  causes  the  marble  to  roll  ? 


If  the  board  were  inclined  more,  would  the  marble  roll 
faster  ? 


In  what  position  must  the  board  be  placed  in  order  that 
the  marble  shall  roll  fastest  ? 


In  the  last  case  the  marble  will  fall  freely,  and  the  distance  will  be 
1 6.08  feet  during  the  first  second. 

Exp.  28.    Drop  a  penny  and  a  piece  of  paper  side  by 
side.     Which  falls  the  faster  ? 


30  CENTER   OF   GRAVITY —  FALLING    BODIES. 

Exp.  29.  Place  a  feather  and  a  penny  in  a  closed  glass 
tube  having  a  stopcock  at  one  end.  Exhaust  the  air,  and 
let  the  two  objects  fall  from  one  end  of  the  tube  to 
the  other. 


Why  does  the  penny  of  Exp.  28  fall  faster  than 
the  paper  ? 


What  force  causes  bodies  to  fall  ? 


Fig. 


VI. 

PENDULUMS. 

Experiment  30.  Using  the  stone  and  string  of  Fig.  10, 
let  the  stone  swing  through  a  distance  of  6  inches.  While 
it  is  swinging,  learn  the  following  definition  : 

Definition.  —  A  Pendulum  is  a  mass  so  suspended  that  it 
may  swing  freely  to  and  fro. 

When  the  stone  (called  the  bob)  is  pulled  to  one  side, 
what  force  causes  it  to  swing  back  ? 


Why  does  it  not  stop  swinging  when  it  gets  back  to  its 
lowest  position  ? 


Exp.  31.  Count  the  number  of  vibrations  (or  swings)  of 
your  pendulum  for  one  minute.  Then  make  the  vibra- 
tions 12  inches  long  instead  of  6  inches,  and  ascertain 
if  the  number  of  vibrations  is  the  same  as  at  first. 


PENDULUMS. 


Exp.  32.  Make  two  pendulums  of  the  same  length,  one 
having  a  bob  of  stone  and  the  other  of  yarn.  Do  different 
materials  affect  the  number  of  vibrations  ? 


Exp.  33.  Make  two  pendulums,  one  10  inches  long  and 
one  40  inches  long.  Count  the  vibrations  of  each  for  one 
minute. 

The  first  vibrates times. 

The  second  vibrates times. 

The  length  of  a  pendulum  made  of  bob  and  string  is 
(for  the  purposes  of  this  book)  the  distance  from  the  point 
of  suspension  of  the  string  to  the  C.  G.  of  the  bob. 

A  pendulum  must  be  39.1  inches  long  in  order  to  vibrate  once  a 
second  at  the  sea  level  in  New  York  City. 

THE    LAW    OF    THE    PENDULUM. 

The  lengths  of  two  pendulums  are  proportional  to  the  squares  of 
the  times  of  their  vibrations. 

If  two  pendulums  require  i  and  2  seconds,  respectively, 
to  vibrate,  how  long  is  the  second  pendulum  compared 
with  the  first  ? 


How  many  inches  long  is  the  second  pendulum  ? 


QUESTIONS   IN   REVIEW.  33 

How  long  must  a  pendulum  be  in  order  to  vibrate  once 
in  4-  a  second  ? 


SUMMARY    OF    CHAPTERS    IV.,    V.,    AND    VI. 


Work. 
Force. 
Gravity. 
Weight. 


Center  of  Gravity. 
Falling  Bodies. 
Pendulums. 


QUESTIONS    IN   REVIEW. 

1 .  Are  molecules  of  ice  smaller  than  those  of  water? 

2.  When  is  work  done? 

3.  What  is  meant  by  resistance? 

4.  What  work  is  done  by  heat  in  a  steam  engine? 

5.  What  work  do  your  muscles  perform  when  you  walk  up  a  hill, 
or  up  stairs  ? 

6.  When  is  gravitation  between  two  masses  strongest? 

7.  If  you  were  at  the  North  Pole,  would  you  weigh  more  or  less 
than  at  present?     Why? 

8.  If  you  rub  two  objects  together,  does  your  muscular  force  meet 
with  resistance? 

9.  Define  friction. 

10.    State  the  difference  between  the  mass  and  the  weight  of  a  body, 
n.    Two  objects  are  of  the  same  size  and  shape  ;  how  may  one  find 
out  whether  or  not  they  are  of  the  same  mass? 

12.    A  falling  body  moves  how  far  during  the  first  second  of  its  fall? 


During  the  second  second? 
During  the  third  second  ? 


During  the  fourth  second? 
HAR.  PHYS.  —  3 


-,,                             QUESTIONS   IN   REVIEW. 
During  the  first  two  seconds? --- 
During  the  first  three  seconds  ? .  -  - 
During  the  first  four  seconds? 


13.  A  clock  in  Washington,  D.C.,  loses  a  very  little  time  each  day ; 
to  what  place  might  the  owner  carry  it  so  that  it  would  keep  correct 
time  without  being  changed  except  in  position? 

14.  What  must  be  the  length  of  a  pendulum  to  beat  once  in  three 
seconds  ? 

15.  Why  should  a  body  be  at  rest  when  its  C.  G.  is  supported? 

16.  Why  do  a  penny  and  a  feather,  when  in  a  vacuum,  fall  together? 


17.  In  what  direction  does  gravity  act? 

Ans.  In  a  straight  line  connecting  the  C.  G.  of  a  body  with  the 
center  of  the  earth. 

18.  What  causes  friction? 

19.  When  is  friction  greatest? 

20.  Why  are  axles  greased? 

21 .  Can  you  mention  any  case  in  which  friction  is  useful? 

22.  Name  some  force  which  acts  at  a  distance.     Illustrate. 

23.  Why  are  the  legs  of  a  chair  farthest  apart  at  their  lower  ends? 

24.  Why  may  a  load  of  hay  be  easily  tipped  over? 

25.  Why  is  a  man  easily  tipped  over  if  his  feet  are  near  each  other? 

26.  What  is  the  only  thing  that  affects  the  number  of  vibrations  of 
a  pendulum  which  is  not  moved  from  place  to  place  on  the  earth  ? 

27.  Where  will  a  pendulum  vibrate  the  faster,  at  the  North  Pole  or 
in  Washington? 


VII. 

LEVER-WHEEL   AND   AXLE- PULLEY. 

Experiment  34.  With  sugar  tongs  lift  a  lump  of  sugar. 
Cut  some  cloth  with  scissors.  Notice  a  steam  engine  at 
work. 

The  tongs,  scissors,  and  engine  enable  forces  to  do  work 
easily  and  conveniently. 

Definition.  —  A  Machine  is  an  instrument  which  enables 
forces  to  do  work  easily  and  conveniently. 

Exp.  35.  Obtain  a  stiff  wooden  stick  about  I  foot  long, 
i  inch  wide,  and  ^  of  an 
inch  thick.  Bore  a  small 
hole  just  over  its  C.  G.,  as 
represented  in  the  figure. 
Insert  in  the  hole  a  short, 
stiff  wire  (to  fit  the  hole 
tightly),  and  rest  the  ends 
of  the  wire  on  supports.  Fig.  12. 

Explain  why  the  bar  remains  in  a  horizontal  position. 
(See  Exp.  26.) 


Definition.  —  A  Lever  is  a  stiff  bar  which  can  be  moved 
about  a  fixed  support  called  the  fulcrum  (FF,  Fig.  12). 
35 


36  LEVER  — WHEEL   AND   AXLE  — PULLEY. 

Exp.  36.  Place  a  5-cent  piece  on  the  lever,  5  inches  from 
the  fulcrum ;  find  out  how  many  similar  coins  must  be 
placed  at  5  inches  from  the  fulcrum  (on  the  other  end  of  the 
lever)  in  order  to  balance  the  first  coin  ;  at  2\  in. ;  i^  in. 

ist ._  2d  ...3d... 

It  is  evident  that  the  weight  of  the  one  5-cent  piece  x  5  equals  the 
weight  of  the  two  5-cent  pieces  x  2|,  or  the  four  5-cent  pieces  x  i^. 

To  use  a  lever,  a  certain  intensity  of  force  must  be  applied  at  one 
point  in  order  to  balance,  or  overcome,  a  resistance  applied  at  some 
other  point.  In  each  case  in  Exp.  36,  the  pull  of  the  coin  (caused  by 
gravity)  on  one  side  of  the  fulcrum  was  the  force  which  balanced  the 
resistance  made  by  the  pull  of  the  coins  on  the  other  side. 

Let  F  stand  for  force,  R  for  resistance,  and  fm  for 
fulcrum. 

THE    LAW    OF    THE    LEVER. 

The  F  X  its  distance  from  the  fulcrum  equals  the  R  x  its  dis- 
tance from  the  fulcrum  when  the  lever  is  in  equilibrium. 

Relatively  to  Fand  R,  there  are  three  positions  for  the 
fm.  Hence  there  are  three  kinds  of  levers  : 

-  In  the  first  kind  the  fm  is  between 

ijjj  Ff     F  and  R. 

.^       (Resistance    is    sometimes    called 

A* T— ?    load.) 

In  the  second  kind  R  is  between 

_t£ F  and  the  fm,  and  F  must  act  in  a 

RJM    direction  opposite  to  that  of  R. 

In  the  third  kind  F  is  between  R 
and  the  fm,  and  must  act  in  a  direction  opposite  to  that 

The  same  law  applies  to  all  forms  of  levers. 


THE    LEVER. 


37 


Exp.  37.  Experiment  with  a  lever  of  the  second  kind. 
Keep  the  wire  fm  in  the  same  place  as  at  first,  so  that  the 
weight  of  the  wood  on  one  side  may  balance  that  of  the 
wood  on  the  other  side.  Apply  F  by  .means  of  a  spring 
balance,  and  make  R  I  pound.  }  Observe  whether  or  not 
the  results  conform  to  the  law.  ' 

This  experiment  may  be  repeated,  using  other  resistances. 

Results.  K'F  of  . .  j?~ .  Ib.  at  5  in.  balances  a  R  of . .  /_ . .  Ib. 
at  2^  in. ; 

whence x  5  = x  2^-. 

A  F  of Ib.  at  4  J  in.  balances  a  R  of Ib.  at  I  in. ; 

whence x  4}  = x  i . 

Exp.  38.    Repeat  Exp.  37,  using  a  lever  of  the  third  kind. 

Results.    A  F  of Ib.  at  2  in.  balances  a  R  of Ib. 

at  4  in. ; 

whence x  2  = x  4. 

A  F  of Ib.  at  i^  in.  balances  a  R  of Ib.  at  4^  in. ; 

whence x  i| -  = x  4j. 

To  which  kind  of  levers  does  each  of  the  following 
belong : 

Scissors? Balance? Wheelbarrow  ? 

Crowbar  ? Nutcracker  ? Sugar  tongs  ? 

Forearm? ..       .__Bootjack? An  oar? J. 


38  LEVER- WHEEL  AND   AXLE -PULLEY. 


Outlines  of  some  common  forms  of  levers.    Arrows  indicate  directions  of  forces. 
Fig.   14. 

Exp.  39.  Obtain  a  large  spool,  and  by  means  of  plugs 
fasten  a  stiff  iron  wire  in  position  (Fig.  15).  Bend  one 
end  of  wire  to  form  a  crank.  Rest  this  wire  on  two 
supports  made  of  tin  or  wood,  and  tack  these  supports  to 
a  board.  Wind  a  thread  around  the  spool,  and  from  the 
loose  end  suspend  a  weight  of  about  6  ounces.  Suspend 
from  the  handle  of  the  crank,  kept  in  a  horizontal  posi- 
tion, a  weight  sufficient  to  keep  the  spool  from  turning. 

Result.   This  weight  is ounces. 


THE   WHEEL   AND   AXLE. 


39 


Definition.  —  A  Wheel  and  Axle  is  a  machine  in  which 
a  spool  or  spindle  (called  axle)  is  turned  by  means  of  a 
crank  or  wheel  in  order  that  a  weight  suspended  from  the 
axle  may  be  lifted. 

This  machine  is  sometimes  called  a  windlass. 


Fig.  15. 

In  the  above  machine,  how  does  R  compare  with  F? 

Ans.  R  is  . times  as  large  as  F. 

How  does  the  radius  of  the  circle  through  which  the 
F  moves  compare  with  the  radius  of  the  wheel  ? 

Ans.  It  is times  as  long. 


LAW  OF  THE  WHEEL  AND  AXLE. 

F  x  the  radius  of  the  wheel  equals  R  x  the  radius  of  the  axle 
when  the  machine  is  in  equilibrium. 

Can  you  name  any  advantage  one  might  gain  in  using 
a  wheel  and  axle  in  lifting  weights  ? 


LEVER  — WHEEL   AND   AXLE  — PULLEY. 


The  capstan  of  a  ship  is  of  what  value  to  the  sailor  ? 


Tell,  if  you  can,  how  the  wheel  and  axle  is  used  in  a  derrick. 


Exp.  40.  Obtain  two  small 
clothesline  pulleys.  Suspend 
one  of  them  from  some  firm 
support,  pass  the  string  over 
the  wheel,  and  attach  a  known 
weight  to  one  end  of  it.  By 
means  of  a  spring  balance  as- 
certain if  anything  has  been 
gained  by  this  machine. 

No  force  has  been  gained  ; 

but  __ 


Fig.  16. 


THE    PULLEY.  41 

Definition.  —  A  Pulley  consists  of  a  wheel  and  a  block, 
the  wheel  being  movable  on  a  pivot  in  the  block. 

The  pulley  of  Fig.  16  is  called  a  fixed  pulley,  and  is  used  in  a  great 
variety  of  ways. 

Exp.  41.    By  means  of  a  string,  attach  a  spring  balance 
to  a  board  loaded  to  weigh  about  6  pounds.    Pull  on  the 


Fig.  17. 

balance,  and  record  the  pull  required  to  just  move  the 
board  on  the  horizontal  table. 


Exp.  42.  Pass  the  string  around  a  fixed  pulley,  and 
pull  on  the  balance  in  different  directions  with  just  force 
enough  to  move  the  board,  as  in  Exp.  41. 


What  is  gained  by  using  a  fixed  pulley  in  this  case  ? 


42 


LEVER  — WHEEL   AND   AXLE  — PULLEY. 


Draw  a  picture  to  represent  a  method  of  lifting  boxes  to 
a  height  of  two  or  three  stories. 


What  is  gained  by  using  two  fixed  pulleys  in  this 


THE    PULLEY.  43 

Exp.  43.  In  Fig.  18  a  fixed  pulley  (£)  is  used.  There  is 
also  used  a  movable  pulley  (a).  By  means  of  a  spring 
balance  observe  if  any  ad- 
vantage, not  found  in  the 
fixed  pulley,  can  be  found 
here. 


ist 


How  large  is  F  when  R  is 
50  pounds  ? 

How  large  is  R  when  F  is 
100  pounds  ? 

.2d 


Do  you  think  that  by  increasing  the  size  of  the  wheel 
you  would  increase  the  advantage  gained  by  using  a  mov- 
able pulley  ? 


Draw  a  figure  similar  to  Fig.  18,  but  putting  the  end 
of  the  cord  marked  c  around  a  second  fixed  pulley,  and 
attach  it  to  the  top  of  the  block  marked  d.  With  such  an 
arrangement,  what  is  the  relation  of  R  to  Ft 


Ans.    R  is  ...  ._.  times  F. 


44  LEVER  — WHEEL   AND   AXLE  — PULLEY. 


THE    LAW    OF    THE    PULLEY    WHEN    IN    EQUILIBRIUM. 

R  equals  F  multiplied  by  the  number  of  strings  which  hold  ft. 

In  lifting  a  load  with  the  apparatus  of  Fig.  16,  how  fast 
does  R  move  compared  with  F? 


How  would  it  be  with  the  apparatus  of  Fig.  18  ? 


In  the  case  of  the  wheel  and  axle  (Fig.  15),  which  moves 
the  faster,  R  or  F? 


What  is  gained  by  using  simple  machines  ? 
A  small  F ... 


What  is  lost  in  using  simple  machines  ? 
Ans.   Time. 

SUMMARY    OF    CHAPTER    VII. 


The  Lever. 

The  Law  of  the  Lever. 
The  Three  Kinds  of  Levers. 
The  Wheel  and  Axle. 


The  Law  of  the  Wheel  and 

Axle. 

The  Pulley. 
The  Law  of  the  Pulley. 


Some  practical  applications  of  machines. 
Fig.  19. 


46  LEVER -WHEEL   AND    AXLE— PULLEY. 


QUESTIONS   IN   REVIEW. 

1 .  Why  are  the  engines  of  a  steamship  placed  as  low  as  possible  ? 

2.  A  man  walking  a  tight  rope  generally  carries  a  long  curved  pole 
loaded  at  the  ends ;  what  advantage  in  using  such  a  pole? 

3.  How  fast  will  a  28-inch  pendulum  swing  when  compared  with  a 
7-inch  pendulum? 

4.  Does  any  one  know  the  size  of  a  molecule? 

5.  Why  are  wheels  used,  and  not  runners,  for  wagons? 

6.  When  will  a  lever  of  the  first  kind  be  balanced  if  R  is  twice  F  ? 

7.  In  what  form  of  lever  must  I  use  a  bar  of  wood  if  I  wish  by 
means  of  it  to  make  a  certain  force  balance  as  great  a  load  as  possible  ? 

8.  Can  a  machine  create  power? 

9.  Why  is  there  loss  of  force  when  it  is  applied  by  means  of  a 
machine? 

(It  is  evident  that  the  weight  of  the  movable  pulley  should  be  con- 
sidered as  a  part  of  the  load.  In  previous  examples  such  weight  has 
been  left  out  of  account.) 

10.  With  the  pulley  of  Fig.  18,  how  great  a  load  could  you  balance 
by  pulling  down  on  the  rope  marked  F,  supposing  the  pulley  a  to  weigh 
10  pounds? 

1 1 .  Suppose  the  movable  pulley  to  weigh  2  pounds  and  F  to  be  2 
pounds ;  what  would  happen  if  2  pounds  were  attached  to  the  mov- 
able block  ?  if  i  pound  were  attached  ?  3  pounds  ? 

12.  May  the  wheel  and  axle  be  considered  as  one  form  of  lever?     If 
so,  what  represents  the  force  arm?   what  the  weight  arm?   what  the 
fulcrum  ? 

13.  In  the  machine  represented  in  Fig.  18,  how  far  would  F  have  to 
move  in  order  to  lift  the  load  2  inches  ? 

14.  What  advantage  is  gained  in  using  a  fixed  pulley  instead  of  a 
round  peg? 


VIII. 

ATMOSPHERIC  PRESSURE-PRELIMINARY  EXPERIMENTS. 

Experiment  44.  Put  one  end  of  a  small  glass 
tube  into  water,  and  then  close  the  upper  end 
of  the  tube  with  the  finger.  Slowly  lift  the  tube 
while  the  upper  end  is  closed. 

I 

Fig.  20. 


Exp.  45.  Fill  a  tumbler  with  water, 
and  place  a  piece  of  thick  paper  on 
the  top.  While  holding  the  paper  in 
place  with  the  left  hand,  invert  the 
tumbler  with  the  right  hand.  After 
inversion,  remove  the  left  hand. 


Fig.  21. 


If  the  water  should  fall  out,  and  no  other  matter  should  occupy  the 
space  in  the  tumbler,  there  would  be  a  vacuum  in  the  tumbler.  Nature 
does  not  willingly  consent  to  such  an  arrangement,  and  therefore  pro- 
vides means  of  keeping  the  water  in  the  tumbler. 

In  Exps.  44  and  45,  what  holds  the  water  in  place  ? 


47 


ATMOSPHERIC   PRESSURE. 
Why  is  the  paper  needed  in  Exp.  45  and  not  in  Exp.  44  ? 


Why  does  a  liquid  flow  from  an  inverted  bottle  in  an 
unsteady  stream  ? 


Exp.  46.  Punch  a  small  hole  in  the  bottom  of  a  tin  can 
(tomato  or  fruit  can).  Repeat  Exp.  45,  using  the  tin  can, 
keeping  the  finger  tightly  pressed  upon  the  hole. 

After  the  can  is  .inverted  and  the  left  hand  has  been 
removed  from  the  paper,  remove  the  finger  from  the  hole. 


In  Exp.  46,  why  does  the  water  fall  after  the  finger  has 
been  removed  ? 


What  causes  air  to  have  weight  ? 


ATMOSPHERIC   PRESSURE. 


49 


Definition.  —  Pressure  due  to  weight  of  air  is  called 
Atmospheric  Pressure,  and  equals  about  15  pounds  per 
square  inch. 

If  one  end  of  the  small  tube  (Exp.  44)  be  put  into  water,  and  some  air 
be  sucked  out  from  the  other  end,  water  will  rise  to  take  the  place  of 
the  air.  The  pressure  of  the  outside  air  on  the  water  of  the  jar  forces 
water  to  rise  into  what  would  otherwise  be  a  partial  vacuum. 

Draw  a  picture  in  explanation  of  the  principle  of  the 
pneumatic  inkstand. 


HAR.  PHYS. — 4 


IX. 


ATMOSPHERIC  PRESSURE-THE  SIPHON. 

Experiment  47.  Bend  a  glass  tube  (see  Appendix)  to 
the  shape  of  a  U,  but  make  one  end  a  little  longer  than 
the  other.  Fill  the  tube  with  water  and  invert  it,  keep- 
ing the  long  arm  closed  with  the  finger.  Place  the 
short  arm  in  a  jar  of  water,  and  remove  the  finger 
from  the  long  arm. 


-    Fig.  22. 

When  the  finger  is  on  the  open  end  of  the  long  arm 
(before  putting  the  siphon  in  water),  why  does  not  the 
water  flow  from  the  short  arm  ? 


Fig.  23. 

If  the  finger  should  be  removed  from  the 
long  arm  before  the  siphon  is  placed  in  water,  would  the 
5° 


THE   SIPHON. 


water  flow  from  the  siphon  ?     If  so,  from  which  arm,  and 
why? 


After  the  siphon  is  placed  in  the  jar  (Fig.  23),  how  long 
does  water  flow  ? 


Exp.  48.    Repeat  Exp.  47,  but  putting  the  long  arm  in 
the  jar  of  water. 

How  long  does  water  flow  from  the  outer  arm  ? 


What  causes  the  siphon  to  operate  ? 

Ans.  The  water  in  the  long  arm  is  heavier  than  that  in 
the  short  arm  ;  it  therefore  falls,  and  the  water  in  the  short 
arm  follows,  while  air  pressure  on  the  water  in  the  jar 
forces  water  up  to  take  the  place  of  the  water  which  has 
been  pulled  over  into  the  long  arm. 


52  ATMOSPHERIC   PRESSURE. 

The  short  arm  is  that  portion  of  the  tube  between  the  bend  and  the 
surface  of  the  water  in  the  jar.  That  portion  of  the  tube  in  the  water 
is  of  use,  however,  because,  as  the  level  of  the  water  is  lowered,  the 
short  arm  will  have  its  end  always  in  water.  Of  course  the  short  arm 
is  being  lengthened  as  long  as  water  flows  through  the  siphon. 

For  what  are  siphons  used  ? 


What  would  be  the  effect  of  making  a  hole  in  the  outer 
arm  (Fig.  23)  at  the  level  of  the  water  in  the  jar  ? 


Find  (in  some  geography)  a  picture  of  an  intermittent 
spring,  and  explain  the  principle  involved. 


X. 


ATMOSPHERIC  PRESSURE- PUMPS   FOR   LIQUIDS. 

Experiment  49.  Fit  a  small  glass  tube  (a)  to  a  round 
cork  which  will  plug  the  lower  end  of  an  argand  lamp 
chimney.  Cut  a  second  piece  of  cork  to 
such  a  size  that  while  fitting  closely  it  will 
move  easily  up  and  down  in  the  chimney ; 
then  fasten  a  rod  (R)  to  this  cork.  In  each 
cork  make  a  small  hole,  and  cover  each 
hole  with  a  small  piece  of  leather  (thin), 
which  should  be  held  in  place  by  a  pin  near 
the  edge.  You  have  now  a  suction  pump 
consisting  of  a  cylinder,  a  piston  (/*),  a  pis- 
ton rod  (R),  and  two  valves  —  one  at  the  bot- 
tom of  the  cylinder  and  one  in  the  piston. 
A  spout  (<£)  may  be  fitted  into  a  cork  cover ; 
the  siphon  tube  may  be  used  here. 


Fig.  24. 


Definition.  —  A  Suction  Pump  is  a  machine 
by  means  of  which  a  liquid  is  drawn  into  a 
cylinder,  and  then  lifted  out  of  the  cylinder  through  a 
spout. 

Write  a  composition  explaining  the  working  of  a  suction 
pump. 

53 


ATMOSPHERIC   PRESSURE. 


THE    SUCTION    PUMP. 


THE   FORCE   PUMP. 

Exp.  50.  Repeat  Exp.  49,  bu"  put 
the  spout  at  the  bottom  of  the  cyl- 
inder instead  of  at  the  top,  and  p  t 
the  outlet  valve  in  the  spout  instead 
of  in  the  piston.  This  arrangement 
is  called  a  force  pump. 

Definition.  —  A  Force  Pump  is  a  ma- 
chine by  means  of  which  a  liquid  is 
drawn  into  a  cylinder,  and  then  forced 
to  a  high  level. 

Write  a  composition  explaining  the 
working  of  a  force  pump. 


55 


Fig.  25. 


THE    FORCE    PUMP. 


ATMOSPHERIC   PRESSURE. 


In  these  pumps,  why  does  water  enter  the  cylinder 
through  the  valve  V  when  the  piston  is  moved  up  ?  (See 
note,  p.  49.) 


From  what  depth  (below  the  piston)  may  water  be  raised 
by  a  suction  pump  ? 

Ans.  From  about  34  feet.  This  is  because  the  weight 
of  a  vertical  column  of  water  34  feet  in  length  equals  the 
weight  of  a  column  of  air  of  the  same  size  (not  height). 
(See  Definition,  p.  49.) 


THE   FORCE   PUMP.  57 

To  what  height  may  water  be  forced  by  a  force  pump  ? 


Force  pumps  are  often  worked  by  an  engine  instead  of 
by  hand. 

A  steam  fire  engine  is  no  more  nor  less  than  a  powerful 
force  pump.  The  water  drawn  is  either  from  an  ordinary 
well  or  from  a  hydrant. 


XI. 


ATMOSPHERIC  PRESSURE-PUMPS   FOR  GASES. 

Definition.  —  The  Air  Pump  is  a  machine  for  removing 
air  (or  other  gas)  from  a  jar. 


Fig.  26. 


Fig.  27. 


This  pump  is  constructed  like  the  suction  pump  for 
liquids,  except  that  at  the  top  of  the  cylinder  it  has  a  valve 
(T)  instead  of  a  spout. 

Experiment  51.  Place  a  hand  glass  on  the  pump  plate, 
ab,  having  first  tied  a  piece  of  sheet  rubber  over  the 
smaller  opening.  Slowly  work  the  pump  handle. 


THE   VACUUM   FOUNTAIN. 


59 


Exp.  52.    Repeat    Exp.    51,    placing   the    palm   of   the 
hand  (instead  of   the  sheet  rubber)  on  the  hand   glass. 


Fig.  28. 


Exp.  53.  Through  the  base  of  a 
long  glass  vessel  pass  a  "fountain 
tube."  Remove  the  air  from  the 


Fig.  29. 

vessel,  close  the   stopcock,  put  the  lower  end  in  water, 
and  open  the  stopcock. 


6o  ATMOSPHERIC   PRESSURE. 


The  vacuum  fountain  may  be  illustrated  by  filling  a  bottle  with 
ammonia  gas,  inserting  a  fountain  tube  (glass)  through  a  tightly  fitting 
stopper,  and  inverting,  so  that  the  large  end  of  the  tube  may  be  placed 
in  water. 


Fig.  30.  Fig.  31. 

Or,  by  means  of  a  second  tube,  air  may  be  sucked  out  of  the  bottle 
while  water  rises  in  the  fountain  tube.  The  last  method  is  the  easiest, 
because  neither  air  pump  nor  ammonia  is  required. 

Exp.  54.  Try  to  lift  the  glass  jar  of  Fig.  26  from  the 
pump  plate  after  the  air  has  been  partly  removed. 


In  Exp.  51,  what  caused  the  rubber  to  bulge  into  the  jar? 


In  Exp.  52,  what  caused  the  hand  to  be  held  to  the  jar 
and  the  flesh  to  bulge  in  ? 


THE  AIR  PUMP.  6 1 

Explain  the  result  of  Exp.  53. 


Why  is  it  difficult  to  lift  the  jar  of  Exp.  54  ? 


Write  a  composition  explaining  the  working  of  an  air 
pump. 

THE    AIR    PUMP. 


62 


ATMOSPHERIC   PRESSURE. 


Definition.  —  The  Condenser 
is  a  pump  used  for  forcing  a 
large  amount  of  air  (or  other 
gas)  into  a  small  space.  It 
is  constructed  like  a  force 
pump. 

Write  a  composition  ex- 
plaining the  working  of  a 
condenser. 


Fig.  32. 


THE   CONDENSER.  63 


THE    CONDENSER. 


64  ATMOSPHERIC   PRESSURE. 

Footballs  are  often  filled  by  means  of  a  condenser. 
The  condenser  is  used  also  in  inflating  rubber  tires  of 
bicycles. 

SUMMARY    OF    CHAPTERS    VIII.,    IX.,    X.,    XL 


Atmospheric  Pressure. 
Preliminary  Experiments. 
Amount  of  Pressure. 
The  Siphon. 


The  Suction  Pump. 
The  Force  Pump. 
The  Air  Pump. 
The  Condenser. 


QUESTIONS  IN  REVIEW. 

1.  Where  do  we  find  air? 

2.  What  is  rare  air? 

3.  What  is  dense  air? 

4.  Why  does  an  inflated  balloon  float  in  air? 

5.  What  causes  matter  to  move  into  vacuums? 

6.  What  is  a  valve? 

7.  For  what  practical  purpose  is  an  air  pump  used? 

8.  For  what  practical  purpose  is  a  siphon  used? 

9.  If  in  an  air  pump  (Fig.  26)  the  cylinder  holds  one  quart  of  air, 
and  the  glass  jar  holds  one  quart  of  air,  how  much  air  of  ordinary  den- 
sity would  you  get  out  of  the  jar  in  once  lifting  the  piston?     In  twice 
lifting  the  piston ?    In  three  times  lifting  the  piston?    How  many  times 
must  the  piston  be  lifted  in  order  to  pump  out  f|  of  the  air  in  the  jar? 

10.  Can  all  the  air  be  pumped  out  of  a  jar? 

11.  With  a  condenser,  how  much  air  is  forced  into  a  holder  at 
each  stroke? 

12.  When  the  force  arm  of  a  lever  is  10  inches  long,  and  the  load 
arm  2\  inches  long,  how  far  must  Fmove  in  order  to  lift  /?  I  inch? 

13.  What  kind  of  a  lever  is  each  of  the  following : 

A  door  while  being  opened  ? 

A  shovel  used  in  throwing  dirt? 

A  shovel  used  in  prying  earth  off  a  bank  of  hard  earth  ? 

14.  If  40  pounds  of  direct  pressure  be  required  to  crack  a  nut,  how 
much  pressure  must  be  applied  at  the  end  of  the  handle  of  a  nutcracker 
6  inches  long,  the  nut  being  placed  I  inch  from  the  hinge? 


XII. 

MAGNETISM. 

Experiment  55.    Place    a   loadstone   among   some   iron 
filings.     Then  lift  the  loadstone. 


Exp.  56.  Rub  a  piece  of  steel  against  a  loadstone,  and 
then  place  the  steel  against  the  filings.  (A  knitting  needle 
will  answer  for  this  experiment.) 


Definition.  — A  Magnet  is  something  that  will  attract  iron. 
The  loadstone  (Exp.  55)  is  a  natural  magnet. 
The  steel  (Exp.  56)  is  an  artificial  magnet. 

Exp.  57.    Ascertain  whether  or  not  the  filings  cling  to 
the  middle  as  well  as  to  the  ends  of  a  magnet. 


HAR.   PHYS.  —  5  65 


56  MAGNETISM. 

Exp.  58.  Suspend  your  magnet  by  means  of  a  fine  silk 
thread  (about  I  foot  long);  in  what  direction  do  its  ends 
point  after  coming  to  rest  ? 


Fig.  33. 
Exp.  59.    After  the  magnet  of  Exp.  58 

has  come  to  rest,  hold  one  end  of  a  second  magnet  near 
one  end  of  the  suspended  magnet;  after  the  result  is 
observed,  hold  it  near  the  other  end  of  the  suspended 
magnet. 


Exp.  60.    Repeat  Exp.  59,  using  second  end  of  second 
magnet. 


Definition.  —  The  ends  of  a  magnet  are  called  its  Poles. 
The  end  which  points  north  when  the  magnet  is  suspended 
freely  is  called  its  North  Pole,  and  the  other  end  is  called 
its  South  Pole. 


LAW   OF    MAGNETS.  67 

Exp.  61.  Suspend  the  second  magnet,  and  see  which 
end  is  its  north  pole  and  which  its  south  pole.  Then  find 
out  which  ends  of  the  two  magnets  attract,  and  which 
repel,  each  other. 


NOTE.  —  When  speaking  of  the  direction  in  which  a 
magnet  points,  the  direction  of  pointing  of  its  north  pole 
is  meant. 

LAW    OF    MAGNETS. 


Exp.  62.  Break  a  magnet  into  two  equal  parts,  and 
each  of  these  parts  into  two  equal  parts,  and  ascertain 
whether  or  not  each  of  the  four  pieces  is  a  magnet. 


Exp.  63.    Wrap  a  magnet  in  a  cloth,  and  observe  its 
action  on  the  poles  of  the  suspended  magnet. 


68  MAGNETISM. 

Exp.  64.  Repeat  Exp.  63,  using  a  bottle  instead  of  cloth. 


Exp.  65.    Rub  one  end  of  a  steel  pen  against  a  magnet. 
Test  the  pen  for  magnetism. 


s  y.  Exp.   66.    Place  a  nail  in 

~~  contact  with  a  magnet ;  does 

the  nail  become  a  magnet? 

If  it  becomes  a  magnet,  does  it  remain  so  after  contact  is 
broken  ? 


In  Exp.  65,  which  end  of  the  pen  became  north  pole? 

Ans.    The  end  which  was  rubbed  against  the pole 

of  the  permanent  magnet. 

In  Exp.  66,  which  end  of  the  Jiail  became  south  pole  ? 


PERMANENT    MAGNETS. 


69 


How  is  one  end  of  a  piece  of  steel  made  to  have  north 
polarity  ? 


Out  of  what  metal  must  permanent  magnets  be  made  ? 


Exp.  67.    Suspend    a     Ni  *•  tg N 

small  tack  or  pen  from       .  s  i 

one    pole   of    a   perma-  Figt  35' 

nent  magnet,  and  then  slide  the  opposite  pole  of  a  second 
magnet  over  the  first  one  in  the  direction  of  the  arrow. 


Exp.  68.    Over  a  large  stationary  bar  magnet  pass  a 
small  suspended  magnet  (£  inch  long).      Move  it  slowly 


L> 


Fig.  36. 

from    end   to  end,   and   note   the  different   directions   in 
which  it    points.     The   magnets   should    not   touch   each 


70  MAGNETISM. 

other.     A  short  sewing  needle  magnetized  will  serve  in 
this  experiment. 

A  small  magnet,  so  arranged  that  it  may  rotate  freely, 
is  called  a  Magnetic  Needle  (see  Figs.  33  and  49). 


If  a  magnetic  needle  be  car- 
ried over  the  earth  from  pole 
to  pole,  it  will  stand  almost  ver- 
tically at  either  the  North  or 
South  Pole,  and  will  stand  hori- 
zontally at  the  equator.  Do 
you  think  from  this  that  the 
earth  is  a  magnet  ? 


XIII. 


FRICTIONAL   ELECTRICITY. 

The  glass  tube  used  in  Exp.  44  may  be  used  here. 

The  two  pith  balls  must  each  be  suspended  by  a  fine,  white  silk 
thread  (about  15  inches  long),  which  should  be  tied  to  a  wooden  or  a 
glass  support. 

The  straw  should  be  balanced  as  in  Fig.  33. 

See  Appendix  for  further  directions. 

Experiment  69.  Rub  a  stick  of  sealing  wax  with  flannel, 
and  bring  it  near  (not  touch- 
ing) a  pith  ball. 


Exp.  70.  Rub  a  warm  glass 
rod  with  silk,  and  bring  it 
near  a  pith  ball. 


Fig.  38. 


Exp.  71.    Repeat  Exps.  69  and  70,  using  the  balanced 


straw  instead  of  the  pith  ball. 





FRICTIONAL   ELECTRICITY. 


Exp.  72.  Touch  each  pith  ball  with  the  rubbed  wax 
until  it  flies  from  the  wax,  and  then  bring  the  balls  near 
each  other. 


Exp.  73.    Now  touch  each  ball 
with  the  fingers,  then  touch  one 

ball  with  the  rubbed  wax  and  the  other  with  the  rubbed 
rod,  and  bring  them  near  each  other. 


Fig.  40. 


Exp.  74.  Make  a  small 
paper  hoop,  and  observe 
whether  or  not  it  will  roll 
on  a  table  following  the 
rubbed  wax. 


Exp.  75.  Suspend  the  rubbed 
wax  by  a  string,  and  bring  your 
hand  near  the  end  of  the  wax. 


Fig.  41. 


LAW    OF    ELECTRICITY.  73 

Exp.  76.    Touch  the  pith  balls,  and  then  bring  them 
near  each  other. 


Exp.  77.    Touch  all  parts  of  the  rubbed  wax,  and  then 
bring  your  hand  near  the  end  of  the  wax. 


NOTE.  —  From  the  above  experiments  we  learn  that  a 
body  when  rubbed  by  another  body  presents  peculiar 
qualities.  The  body  is  said  to  be  Charged  with  Electricity. 
A  body  is  said  to  be  Discharged,  or  Neutral,  when  it  does 
not  present  these  peculiar  qualities. 

Definitions.  —  From  Exps.  72  and  73  we  learn  that  there 
seem  to  be  two  kinds  of  electricity. 

The  kind  that  appears  on  glass  rubbed  with  silk  is  called 
Positive  Electricity. 

The  kind  that  appears  on  sealing  wax  rubbed  with  flan- 
nel is  called  Negative  Electricity. 

LAW    OF    ELECTRICITY. 


NOTE.  —  Every  object  in  its  natural  state  is  thought  to 
hold  both  positive  and  negative  electricity. 

When  an  object  is  said  to  be  charged  with  electricity, 
we  understand  that  in  fact  one  kind  has  been  removed 


74  FRICTIONAL  ELECTRICITY. 

and  that  the  other  kind  has  been  left.  For  instance,  we 
remove  positive  electricity  from  wax  by  rubbing  the  wax 
(Exp.  69)  with  flannel ;  we  remove  negative  electricity  from 
glass  by  rubbing  the  glass  (Exp.  70)  with  silk. 

When  an  uncharged  pith  ball  is  brought  near  charged 
wax  (Exp.  69),  the  negative  of  the  wax  influences  the 
positive  of  the  ball  to  collect  on 
that  side  next  the  wax,  and  drives 
the  negative  of  the  ball  to  the 
opposite  side.  The  pith  ball  will 
therefore  have  one  side  charged 
with  positive  electricity  and  the 
other  side  charged  with  negative  electricity.  If  the  pith 
ball  is  allowed  to  touch  the  wax,  the  +  on  the  ball  will 
disappear,  and  the  ball  will  be  wholly  — .  Before  contact 
the  ball  and  wax  attract  each  other;  after  contact  they 
repel  each  other. 

With  which  electricity  is  a  pith  ball  charged  after  being 
brought  in  contact  with  a  glass  which  has  been  rubbed 
with  silk  ? 


Why  did  the  balls  of  Exp.  72  repel  each  other  ? 


Why  did  the  hoop  of  Exp.  74  follow  the  wax  ? 


CONDUCTORS  —  NON-CONDUCTORS. 


75 


Exp.  78.    Rub  a  piece  of  brass  or  iron  rod  with  flannel ; 
is  any  electricity  shown  ? 


Exp.  79.    Repeat  Exp.  78,  after  wrapping  one  end  of  the 
rod  in  white  silk  so  that  the  brass  cannot  touch  the  hand. 


NOTE.  —  In  Exp.  79,  the  brass  rod  was  insulated  electri- 
cally by  the  white  silk. 

We  learn  from  Exps.  69,  70,  78,  and  79  that  electrical 
qualities  are  shown  by  any  substance  that  is  rubbed.  Some 
substances  retain  these  qualities  and  others  easily  lose  them. 

Definitions.  —  A  Conductor  is  a  substance  which  cannot 
retain  electrical  qualities  unless  insulated. 

A  Non-Conductor  is  a  substance  which  easily  retains  elec- 
trical qualities. 

Exp.  80.  Fill  a  tin  plate  (6  inches  in  diameter)  with  seal- 
ing wax,  melting  the  wax  into  the  plate  over  a  stove  (not 
too  hot  a  stove,  because 
the  wax  might  take  fire). 
To  the  middle  of  a  black- 
ing-box cover  attach  a 
glass  handle  (using  wax). 
This  instrument  is  called 
an  Electrophorus,  and  is 
used  for  obtaining  posi- 
tive frictional  electricity.  Fig.  43. 


7g  FR1CTIONAL   ELECTRICITY. 

Exp.  81.  Rub  the  wax  with  flannel,  and  put  the  cover 
on  the  wax  (Fig.  43).  Remove  the  cover  by  its  handle, 
and  test  it  for  electricity.  (Use  pith  ball  charged  with 
negative  electricity  for  testing.) 


Exp.  82.    Repeat  Exp.  81,  but  touch  the  cover  with  the 
finger  just  before  removing  it  from  the  wax. 


The  figure  in  the  margin  represents  the  electrical  condition  of  the 
parts  of  the  electrophones  before  the  cover  is  touched  by  the  finger. 

The  finger  allows  the  -  of 
the  cover  to  disappear ;  then, 
when  the  cover  is  lifted  by  its 
glass  handle,  it  is  found  to  be 
charged  with  +  electricity. 

If  the  tin  plate  be  connected 
with  the  ground  (through  a 
chain  attached  to  a  gas  pipe 
or  water  pipe),  the  charges  on 
the  cover  will  be  more  intense. 


Fig.  44. 

Exp.  83.    Obtain  a  Leyden  jar.     Charge  the  cover  of 
the   electrophorus    several   times,    bringing   it    each    time 


THE    LEYDEN    JAR.  77 

very  near  the   ball  of   the   Leyden   jar.     A  small  spark 
will  be  noticed  at  each  operation.     Shortly,  the  jar  will  be 

charged  with  positive  electricity. 

Now,   holding   the   jar  with  one    hand, 

bring    a   finger   of    the   other    hand   near 

the  knob. 


Exp.  84.    Rub   a   piece  of    ribbon  with 
warm  flannel,  and  hold  it  near  the  wall  of 

^•c— ~  a  room. 

Fig.  45. 


Why  were  the  balls  of  Exp.  72  first  attracted  and  then 
repelled  by  the  wax  ? 


Why  did  they  repel  each  other  after  being  repelled  by 
the  wax  ? 


;8  FRICTIONAL   ELECTRICITY. 

How  may  a  pith  ball  be  charged  and  discharged  ? 


Why  should  the  pith  ball  be  suspended  by  silk  thread  ? 


How  may  we  know  whether  or  not  a  body  is  charged  ? 


How  may  we  know  whether  or  not  a  body  is  negatively 
charged  ? 


EXPERIMENTS    IN    ELECTRICITY. 


79 


SUMMARY    OF    CHAPTERS    XII.    AND    XIII. 


Magnets  —  Natural,  Artifi- 
cial, Poles  of,  and  Law 
of. 

Magnetic  Induction  in  Soft 
Iron  and  in  Steel. 

Action  of  Large  Magnet  on 
Small  Suspended  Magnet. 

Action  of  the  Earth  on  a 
Magnet 


Developing    Electricity 

Wax  and  Glass. 
Charging  Pith  Ball. 
Kinds  of  Electricity. 
Law  of  Electricity. 
Theory  of  Electricity. 
Conductors. 
Non-Conductors. 
Electrophorus. 
Leyden  Jar. 


The  following  are  experiments  which  may  be  performed  in  presence 
of  the  class,  the  teacher  using  a  machine  which  will  generate  electricity 
in  sufficient  intensity. 

Pith  balls  between  metallic  plates. 

A  pointed  conductor  near  candle  flame. 

Charging  a  boy  with  electricity. 

The  electric  whorl. 

The  aurora  tube. 

Electric  bells. 

The  luminous  pane. 

The  luminous  tube. 

Geissler  tubes. 

Discharging  a  Leyden  jar  through  a  line  of  boys. 

Setting  fire  to  ether  or  alcohol. 

The  electric  seesaw. 

Other  experiments  may  be  performed  by  the  teacher  if  he  has  the 
requisite  apparatus. 

Large  text-books  on  physics  explain  in  full  the  experiments  above 
indicated. 


XIV. 

CURRENT   ELECTRICITY. 


Experiment  85.  Obtain  a  good  pocket  compass.    Fasten 
two  pieces  of  wood,  A  and  B,  to  the  ends  of  two  thin  pieces, 


Fig.  46. 

C  and  D.    The  distance  between  A  and  B  should  be  about 

|  of  an  inch  more  than  the  diameter  of  the  compass  box. 

80 


THE   CELL.  8 1 

The  notches  in  the  upper  surfaces  of  A  and  B  should  be  \ 
of  an  inch  wide,  and  deep  enough  to  admit  90  turns  of 
No.  28  insulated  copper  wire.  The  wire  should  now  be 
wound  closely.  When  this  is  finished,  the  compass  box 
should  just  fit  in  between  the  upper  and  under  sets  of 
wires.  Two  screw  cups  complete  this  instrument,  which 
we  will  hereafter  call  a  Galvanoscope. 

The  galvanoscope  when  in  use  should  have  its  wires  parallel  to  the 
north  and  south  line. 

Exp.  86.  Attach  a  copper  wire  to  a  strip  of  copper 
(3  inches  long,  I  inch  wide),  and  one  to  a  similar  strip  of 
zinc.  Place  the  strips  in  a  glass  of  water  which  contains  a 
few  drops  of  vinegar,  and  connect  the  ends  of  the  wires 
with  the  screw  cups  of  the  galvanoscope.  (The  strips 
should  not  touch.) 


Exp.  87.    Repeat  Exp.  86,  using  a  few  drops  of  sulphuric 
acid  instead  of  vinegar. 


NOTE. — This    arrangement    of    acid,    water,    and    two 
metals  is  called  a  Cell.     The  force  that  moves  the  needle 

HAR.    PIIYS.  — 6 


82  CURRENT   ELECTRICITY. 

is  called  Current  Electricity,  and  is  developed  by  a  chemi- 
cal change  in  which  the  zinc  is  acted  upon  by  the  acid. 
+  _  Since  the  zinc  is  active,  it  is  called  the  Posi- 
tive Plate  of  the  cell.  Since  the  copper  is 
passive,  it  is  called  the  Negative  Plate  of 
the  cell. 

The  free  ends  of  the  wires  which  are 
attached  to  the  plates  are  called  Electrodes. 
The  electrode  of  the  zinc  plate  wire  is  nega- 
tive, while  that  of  the  copper  plate  wire  is 
positive.  When  the  electrodes  are  put  in 
contact,  a  current  is  said  to  flow  in  a  complete  circuit, 
and  to  move  from  the  positive  to  the  negative,  as  indi- 
cated in  the  figure. 


Fig.  47. 


PHENOMENA    WITHIN  THE    CURRENT. 

Exp.  88.    Put    one    electrode  against    the    under    side 

of  the  tongue   and  the    other  against    the    top    of    the 
tongue. 


Exp.  89.    Hold  one  electrode  in  one  hand  and  the  other 
in  the  other  hand. 

(A  battery  of  several  cells  will  be  required.) 


PHENOMENA  WITHIN  THE  CURRENT.      83 

Exp.  90.    Insert  a  fine  platinum  wire(i  inch  long)  in  the 
circuit  of  a  two-cell  battery. 


Exp.  91.  Fill  two  test  tubes  with 
acidulated  water,  and  invert  them 
over  flat  platinum  electrodes.  (Melt 
some  tallow  or  wax  upon  the  por- 
tions of  wire  in  the  liquid,  but  leave 
the  platinum  strips  uncovered.) 


Fig.  48. 


Exp.  92.  Fasten  a  silver  coin  to  the  negative  electrode, 
and  place  both  electrodes  in  a  solution  of  copper  sulphate 
(bluestone). 


NOTE. — The  operation  of   Exp.  92    is   called   Electro- 
plating. 


84 


CURRENT   ELECTRICITY. 


PHENOMENA    WITHOUT    THE    CURRENT. 

Exp.  93.    Pass  a  current  from  south  to  north  over   a 
magnetic  needle.  ^ 

~ 


Exp.  94.  Repeat  Exp.  93, 
passing  the  current  from  north 
to  south. 


Fig.  49. 


Exp.  95.    Repeat  Exps.  93  and  94,  but  pass  the  current 
under  the  needle. 


Can  you  now  explain  the  working  of  the  galvanoscope 
of  Exp.  85  ? 


THE    ELECTRO-MAGNET.  85 

Exp.  96.  Around  a  nail  wind  a  few  turns  of  insulated 
copper  wire  (No.  18).  Put  the  wire  in  the  circuit,  and 
test  the  nail  for  magnetism ;  i.e.,  bring  one  end  of  the 
nail  near  the  poles  of  a  needle,  in  turn. 


Exp.  97.    Remove  the  nail  from  the  coil,  and  again  test 
the  nail  for  magnetism. 


Exp.  98.    Repeat  Exps.  96  and  97,  using  a  steel  nail  or 
wire. 


NOTE.  —  A  piece  of  soft  iron  surrounded  by  wire,  as  in 
Exp.  96,  is  called  an  Electro-magnet. 


XV. 

ELECTRICITY   DEVELOPED   BY   MAGNETS  AND   BY  CURRENTS. 

Experiment  99.  Make  a  helix  (ab)  by  winding  some 
insulated  copper  wire  on  a  small  round  stick  (or  pencil), 

making  the  helix 
3  or  4  inches  long. 
Attach  this  helix 
to  the  binding 
posts  of  the  gal- 
vanoscope.  Then 
put  a  magnet  with  a  quick  motion  into  the  helix,  and 
watch  the  needle. 

The  galvanoscope  in  this  and  the  following  experiments  must  be 
placed  2  or  3  feet  away  from  the  helix,  so  as  not  to  be  influenced  by 
anything  except  the  current  which  is  passing  through  it. 


Fig.  50. 


Exp.  100.    Pull  the  magnet  out  quickly. 


86 


THE    INDUCTION    COIL.  87 

Exp.  101.    Reverse   the   magnet,   and  repeat  Exps.   99 
and   loo. 


Exp.  102.  On  a  bobbin  about  2,  inches  long,  wind  2  ounces 
of  No.  32  double-covered  copper  wire.  Around  this  helix  of 
fine  wire  wind  three  or 
four  layers  of  No.  18  cot- 
ton-covered wire.  Con- 


Fig.  51. 


nect  the  ends  of  the  fine 

wire  with    the    galvano- 

scope.     Insert  an  iron  nail  in  the  center  of  the  bobbin  ; 

then  watch  the  needle  as  you  connect  the  ends  of  the 

coarse  wire  with  a  battery. 

The  wires  should  be  wound  neatly  —  as  thread  is  wound  on  a  spool. 


Exp.  103.    After  the  needle  in  Exp.  102  comes  to  rest, 
quickly  break  the  battery  circuit,  and  watch  the  needle. 


88  MAGNETS   AND   INDUCED   ELECTRICITY. 

Exp.  104.    Remove  the  nail  from  the  helix,  and  repeat 
Exps.  102  and  103. 


Exp.  105.    Repeat  Exp.  59,  using  the  helix  of  Exp.  99 
(connected  with  a  battery)  instead  of  the  second  magnet. 
Is  a  helix  through  which  a  current  is  passing  a  magnet  ? 

NOTE.  —  The  last  few  experiments  prove  two  things: 
first,  that  a  coil  (helix)  through  which  a  current  is  passing 
is  a  magnet ;  second,  that  a  helix  when  surrounding  a 
second  helix,  the  ends  of  whose  wires  are  joined  together, 
causes  a  temporary  current  in  the  second  helix  each  time 
the  battery  (or  primary)  current  is  made  and  each  time 
it  is  broken.  Notice  also  that  these  temporary  currents 
alternate  in  direction,  moving  one  way  when  the  primary 
current  is  made  and  the  other  way  when  the  primary 
current  is  broken.  If  the  primary  current  be  made  and 
broken  in  rapid  succession,  there  will  be  a  rapid  succes- 
sion of  temporary  currents  in  the  secondary  coil.  Thus 
we  shall  have  in  the  secondary  coil  what  is  called  an  Alter- 
nating Current  to  distinguish  it  from  the  Direct  Current, 
which  is  always  the  result  of  battery  action. 

Experiments  99-105  will  enable  even  a  young  student  to  under- 
stand the  construction  and  workings  of  Ruhmkorff's  coil,  the  dynamo, 
the  electric  motor,  and  the  telephone. 


«I'W N 


The  Induction  Coil  in  Section. 


Fig.  52.  —The  Induction  Coi 


Fig.  54. —The  Bell  Telephone  in  Section  and  Perspective. 


QUESTIONS.  9I 

Exp.  106.  Repeat  Exp.  89,  using  the  alternating  cur- 
rent of  Ruhmkorff's  coil  instead  of  the  direct  current  of  a 
battery. 


Exp.  107.    Repeat  Exp.  91,  using  an  alternating  current. 


Exp.  108.    Pass  an  alternating  current  through  a  Geiss- 
ler  tube. 


QUESTIONS. 

1 .  May  a  helix  be  as  good  a  magnet  as  a  piece  of  steel  ? 

2.  In  which  direction  does  a  battery  current  flow? 

3.  What  effect  is  produced  on  a  needle  by  changing  the  direction 
of  the  current  which  is  passing  over  it  ? 

4.  What  is  an  electro-magnet?     (See  Exp.  96.) 

5.  State  some  uses  of  an  electro-magnet. 

6.  Name  two  ways  of  making  a  permanent  magnet. 


92 


MAGNETS    AND    INDUCED    ELECTRICITY. 


SUMMARY    OF    CHAPTERS    XIV.    AND    XV. 

Current  Electricity. 


The  Current. 

Cells. 

Phenomena  within  the  Cur- 
rent. 

Water  Decomposed. 

Electroplating. 


Phenomena  without  the  Cur- 
rent. 

Galvanoscope  Explained. 
Electro-magnets. 
Currents  Developed  by  Mag- 
nets. 
Induction  Coil. 


XVI. 


MOVEMENT  OF  LIGHT. 

Experiment  109.  Make  a  large  pin  hole  in  each  of  three 
pieces  of  cardboard,  and  mount  the  boards  so  that  the  pin 
holes  will  be  in  a  straight 
line.  Place  a  flame  op-  i  A 
posite  the  first  hole,  and 
one  eye  opposite  the  last 
hole  in  such  a  position 
that  the  flame  can  be  seen  through  the  holes.  Then  move 
one  of  the  boards  until  the  holes  are  slightly  out  of  line. 

In  what  kind  of  lines  does  the  light  move  ? 


Fig.  55. 


Exp.  110.  Cut  a  hole  i  inch  square  in  a  piece  of  card 
board;  place  the  board  up- 
right and  about  I  foot  from 
a  candle  flame.  Set  a  screen 
twice  as  far  from  the  flame 
as  is  the  hole  (Fig.  56). 

The  image  of  the  hole  is 
how  large  compared  with  the  c> 
size  of  the  hole  ?  Fig.  56. 


93 


94 


MOVEMENT   OF   LIGHT. 


How  large  would  the  image  be  if  the  screen  were  three 
times  as  far  from  the  flame  as  is  the  hole  ? 


If  you  were  in  a  dark  room,  and  should  make  a  small 
hole  through  the  wall,  where  would  you  place  your  eye  in 
order  to  see  the  top  of  some  object  out  of  doors  ? 


Some  object  out  of  doors.  Room. 

Fig.  57. 


In  order  to  see  the  bottom  of  the  object  ? 


In  order  to  see  that  part  of  the  object  farthest  to  the 
right  ? 


Farthest  to  the  left  ? 


Light  entering  the  room  from  an  exterior  object  would 
form  an  image  of  the  object  on  the  wall  opposite  the  hole. 
What  can  you  say  about  such  an  image  ? 


IMAGES. 


95 


How  far  should  the  wall  be  from  the  hole  in  order  that 
the  image  may  be  of  the  same  size  as  the  object? 


If  the  image  be  4  times  as  broad  as  the  object,  how 
far  would  the  wall  be  from  the  hole  ? 


If  the  image  be  16  times  as  large  as  the  object,  how  far 
would  the  wall  be  from  the  hole  ? 


Exp.  111.  Obtain  a  covered  pasteboard  box  about  9  in. 
x  4  in.  x  4  in.  In  one  end  bore  a  hole  i  inch  in  diameter, 
and  cover  the  hole  with  a 
piece  of  thin  leather,  making 
a  pin  hole  in  the  leather.  At 
the  other  end  make  a  small 
hole  for  observation.  Put 
into  the  box  a  tissue-paper 
screen  mounted  on  a  mova- 
ble block.  Allow  light  from  some  object  to  pass  through 
the  pin  hole,  and  move  the  screen  until  the  image  is  dis- 
tinct. This  instrument  is  called  the  pin-hole  camera.  (Pre- 
serve this  camera  for  a  future  experiment.) 


P,  pin  hole  ;  S,  screen  :  E,  eye  hole. 
Fig.  58. 


MOVEMENT   OF    LIGHT. 


When  the  image  is  2  inches  long  and  5  inches  from  the 
pin  hole,  how  far  from  the  pin  hole  is  the  object  which  is  6 
feet  long  ? 

inches. 

When  an  object  is  100  times  as  large  as  its  image,  how  far 
is  it  from  the  hole  when  the  image  is  8  inches  from  the  hole  ? 

..  inches. 


REFLECTION   OF  LIGHT. 
IMAGES    IN    MIRRORS. 

By  reflection  of  light  is  meant  the  rebounding  of  light. 

Exp.  112.    Draw,  with  crayon,   a  straight  line  upon  a 
table;  arrange  a  mirror  perpendicular  to  the  table  and  to 

the  straight  line,  covering 
all  but  about  \  an  inch 
of  the  mirror  with  paper, 
as  indicated  in  the  figure. 
Rest  a  tack  on  its  head 
at  some  point,  as  at  /,  and 
move  the  eye  along  the 
edge  of  the  table  until 
the  image  of  the  tack 
can  be  seen  in  the  mir- 
ror in  the  direction  of 
Em.  Draw  lines  from  E 
and  t  to  m.  These  lines 
represent  the  path  of  one  of  the  rays  of  light  which  radi- 
ate from  the  tack,  tm  represents  the  Incident,  or  striking, 
ray,  while  mE  represents  the  Reflected  ray. 


Side  view- 


ANGLES   OF   INCIDENCE   AND   REFLECTION. 


97 


The  angle  formed  by  the  incident  ray  and  the  perpen- 
dicular (inp)  is  called  the  Angle  of  Incidence.  The  angle 
formed  by  the  reflected  ray  and  the  perpendicular  is  called 
the  Angle  of  Reflection. 

Do  you  notice  any  relation  which  exists  between  the 
angle  of  incidence  and  the  angle  of  reflection  ? 


Exp.  113.    Repeat  Exp.  112,  after  moving  the  tack  out 
of  the  line  tm.     Do  not  erase  any  lines  thus  far  made. 


Exp.  114.  Remove  the  paper  from  the  mirror,  and  put 
the  tack  into  its  first  position  at  /.  Place  the  eye  in  a  new 
position,  as  at  F,  and  mark  on  the  table  the  path  of  the 
ray  by  which  you  now  observe  the  tack.  At  first  you  saw 
the  tack  in  the  direction  Em,  now  you  see  it  in  the  direc- 
tion Fo.  Remove  the  mirror,  and  see  if  you  can  decide 
where  the  image  was. 


HAR.  PHYS.  —  7 


98 


MOVEMENT    OF    LIGHT. 


Exp.  115.    Repeat  Exp.  1 14,  after  putting  the  tack  in 
new  position. 


How  large  are  images  which  are  seen  in  plane  mirrors  ? 


If  you  stand  in  front  of  a  vertical  mirror,  how  near  the 
floor  must  the  bottom  of  the  mirror  be  in  order  that  you 
may  see  the  images  of  your  feet  ? 


REFRACTION    OF    LIGHT. 

By  refraction  of  light  is  meant  the  bending  of  a  ray  of  light. 

Exp.  116.    Arrange  a  penny  in  an  empty  tin  dish  in 
such  a  position  that  it  will  be  invisible  to  a  person  look- 
ing through  a  hole  in  a  cardboard 
mounted   near   the   dish   (Fig.    60).  a\ 

Fill  the  dish  with  water,  and  again 
look  through  the  hole. 


Fig.  60. 


REFRACTION   OF   LIGHT. 


99 


Only  one  (AD)  of  the  many  rays  of  light  leaving  the 
penny  is  represented.     At  what  point  is  the  ray  bent  ? 


Is  the  ray  bent  away  from  the  perpendicular  DC  ? 


When  you  look  at  a  fish  in  a  pond,  is  the  fish  nearer  to 
you  than  it  seems  ? 


You  have  observed  that  a  ray  of  light  moving  from 
water  to  air  is  bent  away  from  the  perpendicular  which 
is  drawn  to  the  surface  of  the  water. 

How  would  a  ray  be  bent  if  it  were  moving  from  air 
into  water  ? 


Exp.  117.    Place  a  piece  of  thick  glass  against  a  straight 
wire  directly  in  front  of  the  eye. 
Does  the  wire  appear  straight  ? 


Move  the  eye  a  little  to  the  right;  does  the  wire  appear 
to  be  straight  or  to  be  broken  ? 


100 


MOVEMENT   OF   LIGHT. 


The  second  drawing  in  Fig.  61  represents  the  glass  and 
wire  as  seen  from  above.  Explain  how  it  is  that  the  wire 
appears  at  i  instead  of  at  W. 


J£- 


Fig.  61. 


Exp.  118.    Hold  a  pencil  obliquely,  and  so  that  half  is 
in  water  and  half  is  out  of  water.     Explain  its  appearance. 


Exp.  119.    Hold  a  burning  glass  so  that  the  sun's  rays 
may  pass   through   it  and  fall   upon   a  piece  of   paper. 


IMAGES  FORMED  BY  A  LENS.         IOi 

Move  the  paper  to  and  from  the  glass  (which  we  will  call 
a  lens)  until  the  image  of  the  sun  is  as  small  as  possible. 


V 

Section  of  lens 
Fig.  62. 

How  many  inches  from  the  lens  is  this  smallest  image  of 
the  sun  ? 

.  _  inches. 


Definition.  —  The  point  where  the  sun's  rays  meet  after 
passing  through  a  lens  is  called  the  Focus  of  the  lens. 

IMAGES  FORMED  BY  A  LENS. 

Exp.  120.    Hold  a  burning  candle  4  or  5  feet  in  front  of 
a  lens,  and  catch  its  image  on  a  paper  screen. 
Is  the  image  as  near  the  lens  as  is  the  focus  ? 


What  do  you  notice  about  the  size  of  the  image  ? 


Move  the  flame  to  and  from  the  lens  until  it  is  in  such  a 
position  that  the  image  is  as  large  as  the  flame.  Compare 
the  distance  of  the  object  from  the  lens  with  the  distance 
of  the  image  from  the  lens. 


I02  MOVEMENT   OF   LIGHT. 

How  near  the  lens  may  you  place  the  candle  and  still 
have  a  fairly  good  image  ? 


Exp.  121.    Hold    the    lens    at    arm's    length,   and    look 
through  it  at  some  object  10  or  12  feet  distant. 


Exp.  122.  Remove  the  piece  of  leather  from  the  box  of 
Exp.  in,  and  see  if  a  good  image  of  exterior  objects  can 
be  caught  on  the  screen  in  the  box. 


Exp.  123.  Hold  the  lens  so  that  it  may  take  the  place 
of  the  leather,  and  observe  results  as  to  size,  clearness, 
position,  and  inversion  of  the  image. 


SUMMARY   OF   CHAPTER   XVI. 


103 


NOTE.  —  The  box,  as  arranged  with  lens  and  screen, 
forms  a  good  camera ;  by  it  one  may  illustrate  some  of 
the  principles  used  in  making  photographs. 


SUMMARY    OF    CHAPTER    XVI. 
Light. 


Moves  in  Straight  Lines. 
Images  through  a  Small 

Hole. 
Reflection  of  Light. 

Images  in  a  Plane  Mirror. 

Angle  of    Incidence  and 

Angle  of  Reflection. 


Refraction  of  Light. 

By  Mediums  with   Plane 

Surfaces. 
By  Lenses. 

Images  formed  by  a  Double 
Convex  Lens. 


XVII. 

VIBRATIONS-SOUND. 


Experiment  124.  Stretch  a  string  tightly  between  two 
fixed  pegs  about  3  feet  apart.  Pull  the  middle  of  the  string 
a  little  to  one  side,  and  let  go  of  it. 


Fig.  63. 
Result.     (To  eye  and  ear. ) 


The  motions  of  the  string  to  and  fro  are  called  Vibra- 
tions. It  will  be  noticed  that  the  molecules  do  not  move 
lengthwise  of,  but  only  transverse  to,  the  string. 

Exp.  125.  Obtain  a  goblet  of  thin  glass,  and  rub  its 
edge  with  your  wet  finger. 


104 


CONDENSATION  —  RAREFACTION. 


105 


Exp.  126.    Probably  the  vibrations  of  the  glass  cannot 
be  seen.     Therefore  suspend  a  pith  ball  against  the  edge 
of  the  goblet  while  it  is  vibrating. 


Fig.  64.    

These  and  similar  experiments  indicate  that  sound  is 
always  the  result  of  vibrations;  and  we  believe  that 
sound  is  caused  by  these  vibrations.  When  the  vibrat- 
ing body  moves  forward  it  strikes  the  molecules  of  air, 


Fig.  65. 

causing  them  to  crowd  together,  and  they  in  turn  push 
against  their  neighbors,  and  so  on.  Thus  a  condensation 
is  made  to  move  outward  in  all  directions  from  the  vibrat- 
ing body.  This  condensation  of  air  molecules  is  followed 
by  a  rarefaction  when  the  vibrating  body  moves  backward. 


I06  VIBRATIONS  — SOUND. 

One  condensation  and  one  rarefaction  constitute  a  sound 
wave.  These  waves  follow  each  other  in  rapid  succession, 
and  affect  the  drum  of  the  ear,  and  we  say  that  we  hear  a 
sound. 

Exp.  127.  Put  your  ear  against  one  end  of  a  log  of 
wood  while  some  one  scratches  the  opposite  end  with 
a  pin. 


Exp.  128.    Make  a  small  hole  in  the  bottom  of  each  of 
two  tin  cans  (mustard  or  pepper  boxes).     Obtain   10  or 


The  String  Telephone. 
Fig.  66. 

12  yards  of  twine,  pass  one  end  through  the  hole  of  one 
can  and  the  other  end  through  the  hole  of  the  second 
can.  Fasten  a  flat  button  (metal,  ivory,  or  bone)  to  each 
end  of  the  string.  When  the  string  is  taut,  conversation 
may  be  easily  carried  on  through  this  string  telephone. 

A    MEDIUM    NECESSARY. 

Exp.  129.  By  means  of  an  iron  rod  passed  through  the 
rubber  stopper  of  an  air-pump  receiver,  suspend  a  vibrat- 
ing bell  in  a  vacuum. 


RESONANCE. 


107 


Exp.  130.    Allow  air  slowly  to  enter  the  receiver  while 
keeping  the  bell  in  vibration. 


Fig.  67. 


There  are  many  experiments  which 
indicate   that  in    the  absence   of   iron, 


wood,  string,  air,  or  some  means  of  transmitting  sound 
waves  from  a  vibrating  body  to  the  ear,  the  ear  is  not 
affected,  and  no  sound  is  heard. 


RESONANCE. 

Exp.  131.  Fasten  two  triangular  strips  of  wood  (a  and  b} 
to  a  very  thin  board  (Fig.  68).  Stretch  a  string  (or 
wire)  tightly  across  these 
supports,  and  fasten  it  to 
small  nails  in  the  ends  of 
the  board.  Repeat  Exp. 
124,  using  this  apparatus.  Fi£-  68. 


io8 


VIBRATIONS  —  SOUND. 


Exp.  132.  Stopper  the  large  end  of  an  argand  lamp 
chimney,  and  over  the  small  end  hold  a  vibrating  tuning 
fork  while  slowly  pouring  in  water. 


Fig.  69. 

NOTE.  —  In  Exp.  131,  the  small  vibrating  string  sets  the 
thin  board  into  vibration.  In  Exp.  132,  the  small  vibrating 
tuning  fork  sets  the  column  of  air  in  the  chimney  into 
vibration.  In  each  case  the  increase  in  the  intensity  of 
sound  is  due  to  the  vibrations  of  the  increased  amount  of 
matter. 

INTENSITY    OF    SOUND. 

Exp.  133.  Repeat  Exp.  131,  pulling  the  string  at  first 
only  a  little  to  one  side,  and  then  pulling  the  string 
considerably  to  one  side.  In  each  case  notice  the  inten- 
sity (loudness)  of  sound. 


INTENSITY   OF    SOUND. 


109 


NOTE.  —  Resonance  causes  intensity  (or  loudness)  of 
sound.  But  intensity  is  more  often  due  to  the  size  of 
the  vibrations.  Thus  if  a  violin  player  moves  his  bow 
across  the  strings  with  much  vigor,  the  sound  produced 
is  loud  mainly  because  the  vibrations  are  large. 


XVIII. 


HEAT -EFFECTS  OF  HEAT. 

Experiment  134.    Fasten  one  end  of  an  iron  rod  (about 
2  feet  long)  on  a  box,  and  in  such  a  manner  that  the  other 

end  shall  rest  against  the 
upper  part  of  a  vertical 
lever.  Heat  the  bar  by 
means  of  an  alcohol  or 
a  Bunsen  flame. 


Fig.  70. 


Exp.  135.  Arrange  a  glass  tube  and  a  flask 
as  in  Fig.  71,  putting  in  enough  water  to  fill 
the  bottle  and  a  small  part  of  the  tube.  Heat 
the  flask  gently  over  the  Bunsen  flame,  and 
notice  (by  means  of  a  paper  index)  any  change. 


Fig.  71. 


TRANSMISSION    OF    HEAT. 


Exp.  136.    Through   a  rubber  stopper  fit  a  bent  glass 
tube  into  the  neck  of  a  flask,  and  put  the  open  end  into  a 


Fig.  72. 

glass  of   water.      Heat  the  flask  by  putting  both   hands 
on  it. 


Exp.  137.    Apply  heat  to  a  piece  of  ice  in  a  tin  dish. 

The  heat  changes  the  ice  into  water,  and  the  water  into 
steam.  That  is,  heat  changes  the  condition  of  matter. 
(See  Exp.  11.) 

What  is  one  general  effect  of  heat  ? 


TRANSMISSION    OF    HEAT. 

Exp.  138.  Hold  one  end  of  a  short  iron  wire,  and  dip 
the  other  end  in  a  basin  of  boiling  water ;  observe  how 
many  seconds  elapse  before  the  fingers  feel  the  heat. 

...  seconds. 


II2  EFFECTS    OF    HEAT. 

Exp.  139.    Repeat  Exp.  138,  using  a  wooden  rod. 


Exp.    140.    Repeat  Exp.  138,  using  a  brass  wire  of  the 
size  and  length  of  the  iron  wire. 


In  Exps.  138-140,  those  molecules  of  the  rods  which 
are  in  contact  with  the  water  become  warm ;  without 
wandering  from  their  places  they  conduct  to  their  neigh- 
bors the  heat  received  from  the  water.  This  method  of 
transmission  of  heat  is  called  Conduction. 

Exp.  141.  Put  some  bits  of  paper 
into  a  flask  half  full  of  water.  Ap- 
ply heat  to  the  bottom' of  the  flask. 


Fig.  73. 


EVAPORATION  — DISTILLATION.  n$ 

In  this  case  the  bits  of  paper  show  that  there  is  molec- 
ular motion  producing  currents  of  water.  The  warmed 
molecules  rise,  thus  actually  transmitting  heat  by  con- 
veying it  from  the  bottom  to  the  top  of  the  water ;  then, 
having  given  it  up,  they  return  for  more. 

All  liquids  and  gases  are  heated  by  Convection. 

Exp.  142.  Stand  a  few  feet  from  a  fire ;  you  will  observe 
that,  while  you  feel  the  heat,  it  reaches  you  neither  by  con- 
duction nor  convection,  but  seems  to  stream  towards  you. 

Here  heat  is  radiated  by  the  fire.  Heat  is  therefore 
said  to  be  transmitted  by  Radiation. 

Exp.  143.    Into  a  test  tube  nearly  filled  with  water  put 
a  piece  of  ice  attached  to  a  sinker.     Apply  heat  near 
the  top  of  the  test  tube  until  the  water 
boils. 


Fig.  74. 


Is  water  a  good  conductor  of  heat  ? 


EVAPORATION DISTILLATION. 

Exp.  144.    Apply  heat  to  the  bottom  of  a  test  tube  half 
filled  with  water.       Dip  the  outer  end  of  delivery  tube 

HAR.  PHYS.  —  8 


1 14 


EFFECTS   OF    HEAT. 


into  water,   and   notice   the   bubbles   which   come    out   of 
the  tube. 


Fig.  75. 

It  will  be  noticed  that  in  case  of  boiling,  only  the  water 
comes  out  of  the  test  tube.  Any  dirt  or  salt,  or  other 
impurity,  is  left  behind  in  the  test  tube.  This  fact  enables 
us  to  obtain  pure  water.  The  process  is  called  Distillation. 

Exp.  145.  Arrange  the  delivery  tube  of  a  boiler  in 
such  a  way  that  its  outer  end  shall  be  in  a  Flor- 


Fig.  76. 

ence  flask  over  which  a  stream  of   cold  water   is   kept 
running. 


SUMMARY. 


SUMMARY    OF    CHAPTERS    XVII.    AND    XVIII. 


Sound. 

Vibrations. 

Of  Strings. 

Of  Glasses. 

Theory  of  Sound  Waves. 
String  Telephone. 
A  Medium  Necessary. 
Resonance. 


Heat. 

Effects  of  Heat. 

On  Solids. 

On  Liquids. 

On  Gases. 
Transmission  of  Heat. 

Conduction. 

Convection. 

Radiation. 
Evaporation  —  Distillation. 


QUESTIONS   IN   REVIEW. 

1 .  Which  is  the  larger,  an  atom  or  a  molecule  ? 

2.  Name  the  three  conditions  of  matter. 

3.  Why  does  an  ivory  ball,  when  dropped  on  stone,  rebound  to 
almost  the  height  from  which  it  started? 

4.  Define  work,  force,  and  gravity. 

5.  What  is  a  vapor? 

6.  Is  paper  flexible  and  elastic? 

7.  Where  on  the  earth  does  matter  weigh  the  most? 

8.  If  a  marble  were  dropped  from  the  edge  of  a  high  roof,  how  far 
would  it  fall  during  the  first  second? 

9.  What  would  be  true  of  a  piece  of  paper  under  the  same  conditions? 

10.  A  pendulum  9.775  inches  long  vibrates  how  many  times  per 
second  at  the  sea  level  in  New  York  City? 

11.  Account  for  the  fact  that  a  piece  of  iron  is  larger  when  warm 
than  when  cold. 

12.  A  marble  rolls  down  an  incline  3  inches  the  first  second;  how 
far  will  it  roll  during  the  third  second?     During  3  seconds? 

13.  Is  there  a  mass  which  has  no  elasticity? 

14.  A  horse  is  moving  a  small  house  by  means  of  four  movable 
pulleys,  and  at  the  rate  of  9  inches  per  second  ;  how  fast  does  the  horse 
walk  per  minute? 

15.  The  crank  of  a  windlass  is  turned  once  a  second;  the  circum- 
ference of  the  axle  is  i  that  of  the  wheel,  and  a  bucket  of  water  is  raised 
I  foot  per  second  ;  what  is  the  circumference  of  the  wheel? 

1 6.  Find  the  distance  through  which  a  stone  falls  in  the  eleventh 
second  of  its  fall. 

17.  What  do  you  understand  by  the  mechanical  advantage  of  a 
machine? 

18.  The  weight  at  one  end  of  a  6-foot  lever  in  equilibrium  is  200 
pounds ;  the  force  is  applied  at  the  other  end,  and  2  feet  from  the  ful- 
crum ;  how  much  is  F? 

19.  Two  men  carry  a  2oo-pound  weight  between  them  on  a  pole  5 
feet  long ;  one  man  carries  only  80  pounds ;  how  far  from  his  hand  is 
the  weight  suspended? 

116 


QUESTIONS    IN    REVIEW.  117 

20.  In  a  system  containing  three  movable  pulleys  and  three  fixed 
pulleys,  the  movable  pulleys  weigh  6  pounds  ;  what  force  must  be  applied 
to  keep  the  system  in  equilibrium  when  no  weight  is  suspended  from 
the  movable  pulleys? 

21.  A  force  produces  a  motion  of  14  feet  per  second  in  one  mass, 
and  42  feet  per  second  in  another  mass ;  compare  the  masses. 

22.  State  some  practical  uses  of  the  wheel  and  axle;  of  the  pulley; 
of  any  combination  of  these  two  machines. 

23.  Suppose  that  the  F  and  R  represented  in  Fig.  18  (p.  43)  are  in 
equilibrium ;  how  would  you  prevent  motion  if  the  F  were  increased  by 
2  pounds?     If  the  R  were  increased  by  2  pounds? 

24.  An  egg  floats  on   brine,   but  sinks  in  water;   which   has  the 
greater  S.  G.,  the  brine  or  the  water? 

25.  In  the  siphon  represented  in  Fig.  23  (p.  50),  what  would  be  the 
effect  of  lengthening  the  long  arm? 

26.  What  would  happen  if  a  hole  were  bored  in  the  long  arm  of  a 
siphon  at  a  point  above  the  level  of  the  water  in  the  jar? 

27.  What  do  you  consider  to  be  the  short  arm  of  a  siphon? 

28.  How  might  you  proceed  to  cover  a  brass  spoon  with  a  layer  of 
silver? 

29.  How  might  you  obtain  hydrogen  from  water? 

30.  Draw  a  diagram  to  show  the  direction  of  flow  of  a  current  out- 
side a  cell,  zinc  and  carbon  being  the  elements  of  the  cell. 

31.  When  the  needle  is  below  a  current  and  is  deflected  towards 
the  west,  what  is  the  current  direction? 

32.  Could  a  dry  silk  cord  be  used  as  a  conductor  for  a  battery? 

33.  How  far  from  the  aperture  represented  at  a  in  Fig.  57  (p.  94) 
must  an  object  be  placed  in  order  that  the  image  may  be  three  times 
the  size  of  the  object? 

34.  In  looking  into  a  room  through  a  window  pane,  do  we  see 
objects  in  their  real  positions?     Explain  your  answer. 

35.  What  is  the  great  source  of  light?     Name  two  other  sources  of 
'light. 

36.  Mention  some  musical  instruments  in  which  air  is  made  resonant. 

37.  Does  every  vibrating  body  produce  sound? 

38.  What  causes  a  pendulum  to  vibrate? 

39.  How  could  you  prove  by  means  of  a  pendulum  that  gravity  is 
greater  at  New  York  than  at  Panama? 

40.  How  does  rubbing  a  coin  on  a  coat  sleeve  affect  the  temperature 
of  the  coin? 


IT8  QUESTIONS    IN    REVIEW. 

41.  What  is  the  great  source  of  heat?     Can  you  name  two  other 
sources  ? 

42.  In  case  light  illuminates  I  square  foot  of  surface  when  the  sur- 
face is  a  short  distance  from  the  source  of  light,  how  much  surface 
would  the  same  number  of  rays  illuminate  at  twice  the  distance?     (See 
Fig.  56,  p.  93.) 

43.  Suppose  you  were  reading  a  book  placed  at  a  distance  of  5  feet 
from  a  light ;  how  many  times  brighter  would  the  page  be  if  you  should 
place  it  2\  feet  from  the  same  light? 


APPENDIX. 


The  teacher  either  should  require  the  pupil  to  perform 
the  following  indicated  experiments  in  the  schoolroom,  or 
should  perform  them  himself  before  his  class : 

Exps.  9,  29,  36-38,  41,  42,  49-54,  80-83,  85-108, 
112-115,  119-121,  123,  129,  130,  132,  134,  141,  143-145. 

Exp.  16.  Pupils  should  club  together  and  buy,  through 
the  teacher,  pieces  of  sheet  lead,  copper,  iron,  and  zinc. 
These  can  be  cut  (with  scissors)  into  strips  about  2  inches 
long  and  |  an  inch  wide. 

Exp.  37.  The  spring  balance  should  weigh  in  ^  pounds 
up  to  8  pounds. 

Exp.  40.  The  teacher  should  buy  small  swivel-tackle 
pulleys  (30^  per  dozen). 

Exp.  44.  The  teacher  should  buy  glass  tubing  by  the 
pound,  allowing  i  pound  for  each  10  pupils.  Tubing  is 
sold  in  lengths  of  about  2  feet,  if  so  requested. 

One  half  the  tubes  (by  number,  not  by  weight)  should 
be  T3g  inch  bore,  and  the  other  half  should  be  T6g  inch  bore. 

Cut  each  tube  into  two  equal  parts,  and  allow  each  pupil 
one  straight  piece  of  ^  inch,  and  one  piece  of  -^  inch 
bent  into  a  siphon  whose  short  arm  is  about  4  inches  long. 

Glass  tubing  is  cut  by  making,  at  the  place  of  cutting, 
a  groove,  using  a  three-cornered  file.  Then,  holding  the 
119 


I20  APPENDIX. 

tube- in  both  hands,  with  the  groove  turned  from  the  body, 
and  holding  the  thumbs  together  behind  the  groove,  push 
gently  outward  with  the  thumbs.  File  the  sharp  edges. 


Fig.  77. 


Glass  tubing  is  bent  by  holding  the  tube  in  a  jet  of  burn- 
ing illuminating  gas.  Keep  the  tube  rotating  so  that  all 
portions  of  the  part  to  be  bent  may  be  heated  equally. 
When  soft,  bend  tube  quickly,  and  allow  it  to  cool  before 
removing  the  soot.  If  a  gas  jet  is  not  convenient,  use 
Bunsen  or  alcohol  flame. 

Exp.  49.  It  will  be  found  much  more  satisfactory  to 
buy  glass  models  of  pumps  than  to  require  each  pupil  to 
make  his  own.  Glass  pumps  of  German  manufacture  are 
sold  at  very  low  rates. 

Exp.  51.  No  school  should  be  without  a  good  air  pump 
and  some  attendant  apparatus.  Prices  vary  from  about 
$15  up. 

Exp.  56.  Let  the  teacher  buy  large  size  knitting  needles 
by  the  dozen,  and  magnetize  them  (four  or  five  at  a  time) 


APPENDIX. 


121 


by  putting  them  into  a  helix  about  7  or  8  inches  long, 
made  by  winding  heavy  (No.  18)  insulated  wire  closely 
around  a  lead  pencil.  Let  the  current  pass  on  the  helix 
wire  for  about  a  half  a  minute. 

Exp.  59.  Sealing  wax  should  be  bought  by  the  pound 
in  sticks  about  8  inches  long  and  |-  an  inch  square.  Pith 
balls  should  be  bought  by  the  dozen.  Straws  should  be 
bought  by  the  package. 

Exps.  80,  83.  Pupils  rarely  succeed  in  making  a  satis- 
factory electrophorus  or  a  Ley  den  jar. 

Exp.  85.  The  pocket  compass  must  be  as  sensitive  as 
can  be  found.  There  is  no  gain  in  attempting  experiments 
with  a  galvanoscope  unless  the  needle  be  of  the  best  work- 
manship. $  1.25  should  be  the  minimum  price. 

Exp.  90.  Grenet  cells  will  be  found 
of  more  advantage  than  any  other  kind. 
Do  not  require  pupils  to  make  their 
own  cells.  The  mixture  for  the  Grenet 
cell  consists  of  10  parts  (by  weight)  of 
sulphuric  acid,  17  parts  bichromate  of 


Fig.  78. 


Fig.  79. 


potash,  and   100  parts  water.      The  "American"  Grenet 
is    low    in    price   ($1.25),    and   will    last    many   years    if 


I22  APPENDIX. 

properly  cared  for.  When  using  two  or  more  cells,  con- 
nect the  zinc  of  one  with  the  carbon  of  the  second,  etc. 
Always  lift  the  zincs  from  the  liquid  when  not  in  use. 

The  following  lists  comprise  the  most  important  pieces 
of  apparatus  required  by  pupil  and  teacher  for  use  with 
this  book.  The  things  not  indicated  are  too  common  to 
need  naming. 

FOR   EACH    PUPIL. 

1  piece  each  of  sheet  lead,  sheet  copper,  sheet  iron,  and 
sheet  zinc  (each  piece  2  inches  by  ^  inch). 

2  pulleys. 

i  foot  glass  tube,  T3g  inch  bore, 
i  foot  glass  tube,  j5g  inch  bore. 

1  piece  sealing  wax,  8  inches  long,  ^  inch  square. 

2  pith  balls. 

2  straws,  each  9  inches  long. 
2  knitting  needles,  No.  10. 


FOR    THE    TEACHER. 

i  convex  lens,  2  inches  in  diameter, 
i  alcohol  lamp  or  Bunsen  burner, 
i  penny  and  feather  tube. 

I  spring  balance,  weighing  to  8  pounds,  and  graduated 
in  |  pounds. 

I  glass  suction  pump. 

i  glass  force  pump. 

i  air  pump  with  glass-stoppered  receiver. 

i  hand  glass. 

i  vacuum  fountain. 


APPENDIX. 


123 


12  rubber,  or  cork,  stoppers,  assorted  sizes,  —  two  holes 
in  each  if  rubber, 
i  small  lodestone. 
Catskin. 
Electrophorus. 
Leyden  jar  (3  pints). 
Pocket  compass. 

1  pound  No.  1 8  double  cotton-covered  copper  wire. 

2  ounces  No.  32  double  cotton-covered  copper  wire. 
^  ounce  No.  28  single  silk-covered  copper  wire. 

2  pounds  sulphuric  acid. 
2  Grenet  cells,  "American." 
6  five-inch  test  tubes. 
\  pound  copper  sulphate. 

1  pound  bichromate  of  potassium. 
Ruhmkorff  s  coil  (^  inch  spark). 
Geissler  tube. 

2  twelve-ounce  Florence  flasks. 
i  rat-tail  file  (6  inches  long). 

1  three-cornered  file  (6  inches  long). 
8  feet  small  brass  chain. 

Piece  platinum  foil,  i  inch  by  \  inch. 
4  inches  fine  platinum  wire. 

2  wood-screw  binding  posts,  single  (smallest  size),  Exp.  85 
Rubber  tissue  (6  inches  square). 

4  double  connectors  (plain). 
Tuning  fork  (6-inch  prongs). 


Typography  by  J.  S.  Cashing  &  Co.,  Norwood,  Mass. 


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Designed   to  serve  as  both    text-book  and   laboratory   manual   in  Qualitative 

Analysis. 


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receipt  of  the  price,  by  the  Publishers: 

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(89) 


Zoology  and  Natural  History 

Gurnet's  School  Zoology 

By  MARGARETTA  BURNET.     Cloth,  i2mo,  216  pages        .     75  cents 

A  new  text-book  for  high  schools  and  academies,  by  a  practical  teacher;  sufficiently 
elementary  for  beginners  and  full  enough  for  the  usual  course  in  Natural  History. 

Needham's  Elementary  Lessons  in  Zoology 

By  JAMES  G.  NEEDHAM,  M.S.     Cloth,  iamo,  302  pages   .     90  cents 

An  elementary  text-book  for  high  schools,  academies,  normal  schools  and  prepara- 
tory college  classes.  Special  attention  is  given  to  the  study  by  scientific  methods, 
laboratory  practice,  microscopic  study  and  practical  zootomy. 

Cooper's  Animal  Life 

By  SARAH  COOPER.     Cloth,  i2mo,  427  pages  .         .         .          $1.25 
An    attractive   book  for  young  people.      Admirably  adapted   for  supplementary 

readings  in  Natural  History. 

Holders'  Elementary  Zoology 

By  C.  F.  HOLDER,  and  J.  B.  HOLDER,  M.D. 

Cloth,  1 2mo,  401  pages $1.20 

A  text-book  for  high  school  classes  and  other  schools  of  secondary  grade. 

Hooker's  Natural   History 

By  WORTHINGTON  HOOKER,  M.D.    Cloth,  i2mo,  394  pages     90  cents 
Designed  either  for  the  use  of  schools  or  for  the  general  reader. 

Morse's  First  Book  in  Zoology 

By  EDWARD  S.  MORSE,  Ph.D.     Boards,  I2mo,  204  pages     87  cents 
For  the  first  study  of  animal  life.     The  examples  presented  are  such  as  are  com- 
mon and  familiar. 

Nicholson's  Text-Book  of  Zoology 

By  H.  A.  NICHOLSON,  M.D.     Cloth,  I2mo,  421  pages     .          $1.38 
Revised  edition.     Adapted  for  advanced  grades  of  high  schools  or  academies  and 

for  first  work  in  college  classes. 

Steele's  Popular  Zoology 

By  J.  DORMAN  STEELE,  Ph.D.,  and  J.  W.  P.  JENKS. 

Cloth,  I2mo,  369  pages $1.20 

For  academies,  preparatory  schools  and  general  reading.      This  popular  work  is 

marked  by  the  same  clearness  of  method  and  simplicity  of  statement  that  characterize 

all  Prof.  Steele's  text-books  in  the  Natural  Sciences. 

Tenneys'  Natural  History  of  Animals 

By  SANBORN  TENNEY  and  ABBEY  A.  TENNEY. 

Revised  Edition.     Cloth,  I2mo,  281  pages         .         .         .  $1.20 

This  new  edition  has  been   entirely   reset  and   thoroughly   revised,   the   recent 

changes  in  classification  introduced,  and  the  book  in  all  respects  brought  up  to  date. 

Treat's  Home  Studies  in  Nature 

By  Mrs.  MARY  TREAT.     Cloth,  I2mo,  244  pages     .         .     90  cents 
An  interesting  and  instructive  addition  to  the  works  on  Natural  History. 


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receipt  of  the  price,  by  the  Publishers  : 

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Geology 


Dana's  Geological  Story  Briefly  Told 

By  JAMES  D.  DANA.     Cloth,  12010,  302  pages    .        .        .     $1.15 

A  new  edition  of  this  popular  work  for  beginners  in  the  study  and  for  the  general 
reader.  The  book  has  been  entirely  rewritten,  and  improved  by  the  addition  of  many 
new  illustrations  and  interesting  descriptions  of  the  latest  phases  and  discoveries  of 
the  science.  In  contents  and  dress  it  is  an  attractive  volume  either  for  the  reader  or 
student. 

Dana's  New  Text-Book  of  Geology 

By  JAMES  D.  DANA.     Cloth,  i2mo,  422  pages    .        .        .     $2.00 

A  text-book  for  classes  in  secondary  schools  and  colleges.  This  standard  work 
has  been  thoroughly  revised  and  considerably  enlarged  and  freshly  illustrated  to 
represent  the  latest  demands  of  the  science. 

Dana's  Manual  of  Geology 
By  JAMES  D.  DANA. 
Cloth,  8vo,  1087  pages.    1575  Illustrations  ....     $5  00 

Fourth  revised  edition.  This  great  work  was  thoroughly  revised  and  entirely 
rewritten  under  the  direct  supervision  of  its  author,  just  before  his  death.  It  is  recog- 
nized as  a  standard  authority  in  the  science  both  in  Europe  and  America,  and  is  used 
as  a  manual  of  instruction  in  all  the  higher  institutions  of  learning. 

Le  Conte's  Compend  of  Geology 

By  JOSEPH  LE  CONTE,  LL.D.     Cloth,  I2mo,  399  pages     .     $1.20 

Designed  for  high  schools,  academies  and  all  secondary  schools. 
Steele's  Fourteen  Weeks  in  Geology 

By  J.  DORMAN  STEELE,  Ph.D.    Cloth,  i2mo,  280  pages    .     $1.00 

A  popular  book  for  elementary  classes  and  the  general  reader. 

Andrews's  Elementary  Geology 

By  E.  B.  ANDREWS,  LL.D.     Cloth,  12010,  283  pages        .     $1.00 

Adapted  for  elementary  classes.  Contains  a  special  treatment  of  the  geology  of 
the  Mississippi  Valley. 

Nicholson's  Text-Book  of  Geology 

By  H.  A.  NICHOLSON,  M.D.     Cloth,  i2mo,  520  pages       .     $1.05 

A  brief  course  for  higher  classes  and  adapted  for  general  reading. 

Williams's  Applied  Geology 

By  S.  G.  WILLIAMS,  Ph.D.    Cloth,  i2mo,  386  pages   .        .     $1.20 

A  treatise  on  the  industrial  relations  of  geological  structure;  and  on  the  nature, 
occurrence,  and  uses  of  substances  derived  from  geological  sources. 


Copies  of  any  of  the  above  books  will  be  sent  prepaid  to  any  address,  on 
receipt  of  the  price,  by  the  Publishers  : 

American  Book  Company 

New  York  ,  *  Cincinnati  .  Chicago 

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Physical   Geography 


Appletons'   Physical   Geography 

By  JOHN  D.  QUACKENBOS,  JOHN  S.  NEWBERRY,  CHARLES  H. 
HITCHCOCK,  W.  LE  CONTE  STEVENS,  WM.  H.  BALL,  HENRY 
GANNETT,  C.  HART  MERRIAM,  NATHANIEL  L.  BRITTON, 
GEORGE  F.  KUNZ  and  Lieut.  GEO.  M.  STONEY. 

Cloth,  quarto,  140  pages  .         .         .         .         .         .         .         $1.60 

Prepared  on  a  new  and  original  plan.  Richly  illustrated  with  engrav- 
ings, diagrams  and  maps  in  color,  and  including  a  separate  chapter  on 
the  geological  history  and  the  physical  features  of  the  United  States. 
The  aim  has  been  to  popularize  the  study  of  Physical  Geography  by 
furnishing  a  complete,  attractive,  carefully  condensed  text-book. 

Cornell's   Physical   Geography 

Boards,  quarto,  104  pages         .         .       -  .         .        -.         ,         $1.12 

Revised  edition,  with  such  alterations  and  additions  as  were  found 
necessary  to  bring  the  work  in  all  respects  up  to  date. 

Hinman's   Eclectic   Physical   Geography 

Cloth,  1 2mo,  382  pages    : $1,00 

By  RUSSELL  HINMAN.  A  model  text-book  of  the  subject  in  a  new 
and  convenient  form.  It  embodies  a  strictly  scientific  and  accurate 
treatment  of  Physiography  and  other  branches  of  Physical  Geography. 
Adapted  for  classes  in  high  schools,  academies  and  colleges,  and  for 
private  students.  The  text  is  fully  illustrated  by  numerous  maps, 
charts,  cuts  and  diagrams. 

Guyot's   Physical   Geography 

Cloth,  quarto,  124  pages $1.60 

By  ARNOLD  GUYOT.  Thoroughly  revised  and  supplied  with  newly 
engraved  maps,  illustrations,  etc.  A  standard  work  by  one  of  the  ablest 
of  modern  geographers.  All  parts  of  the  subject  are  presented  in  their 
true  relations  and  in  their  proper  subordination. 

Monteith's   New   Physical   Geography 

Cloth,  quarto,  144  pages $1.00 

An  elementary  work  adapted  for  use  in  common  and  grammar  schools, 
as  well  as  in  high  schools. 


Copies  of  any  of  the  above  books  will  be  sent  prepaid  to  any  address,  on 
receipt  of  the  price,  by  the  Publishers: 

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(98) 


Laboratory    Physics 


Hammel's  Observation    Blanks   in    Physics 

By  WILLIAM  C.  A.  HAMMEL,  Professor  of  Physics  in 
Maryland  State  School.  Boards,  Quarto,  42  pages. 
Illustrated. 30  cents 

These  Observation  Blanks  are  designed  for  use  as  a 
Pupil's  Laboratory  Manual  and  Note  Book  for  the  first 
term's  work  in  the  study  of  Physics.  They  combine  in 
convenient  form  descriptions  and  illustrations  of  the  appa- 
ratus required  for  making  experiments  in  Physics,  with 
special  reference  to  the  elements  of  Air,  Liquids,  and  Heat; 
directions  for  making  the  required  apparatus  from  simple 
inexpensive  materials,  and  for  performing  the  experiments, 
etc.  The  book  is  supplied  with  blanks  for  making  drawings 
of  the  apparatus  and  for  the  pupil  to  record  what  he  has 
observed  and  inferred  concerning  the  experiment  and  the 
principle  illustrated. 

The  experiments  are  carefully  selected  in  the  light  of 
experience  and  arranged  in  logical  order.  The  treatment 
throughout  is  in  accordance  with  the  best  laboratory  practice 
of  the  day. 

Hon.  W.  T.  Harris,  U.  S.  Commissioner  of  Education, 
says  of  these  Blanks: 

'I  have  seen  several  attempts  to  assist  the  work  of 
pupils  engaged  in  the  study  of  Physics,  but  I  have  never 
seen  anything  which  promises  to  be  of  such  practical  assist- 
ance as  Hammel's  Observation  Blanks." 


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on  receipt  of  the  price,  by  the  Publishers  : 

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